net: mvneta: fix open() error cleanup

If mvneta_mdio_probe() fails, a kernel warning is triggered due to
missing cleanup in the error path.  Add the necessary cleanup.

------------[ cut here ]------------
WARNING: CPU: 1 PID: 281 at kernel/irq/manage.c:1814 __free_percpu_irq+0xfc/0x130
percpu IRQ 38 still enabled on CPU0!
Modules linked in: bnep bluetooth xhci_plat_hcd xhci_hcd marvell_cesa armada_thermal des_generic ehci_orion mcp3021 spi_orion sfp mdio_i2c evbug fuse
CPU: 1 PID: 281 Comm: connmand Not tainted 4.7.0-rc2+ #53
Hardware name: Marvell Armada 380/385 (Device Tree)
Backtrace:
[<c0013488>] (dump_backtrace) from [<c00137d0>] (show_stack+0x18/0x1c)
 r6:60010093 r5:ffffffff r4:00000000 r3:dc8ba500
[<c00137b8>] (show_stack) from [<c02c6fe0>] (dump_stack+0xa4/0xdc)
[<c02c6f3c>] (dump_stack) from [<c002d4ec>] (__warn+0xd8/0x104)
 r6:c081e6a0 r5:00000000 r4:edfe5d50 r3:dc8ba500
[<c002d414>] (__warn) from [<c002d5d0>] (warn_slowpath_fmt+0x40/0x48)
 r10:a0010013 r8:c09356f8 r7:00000026 r6:ef11a260 r5:edd7b980 r4:ef11a200
[<c002d594>] (warn_slowpath_fmt) from [<c008c8e0>] (__free_percpu_irq+0xfc/0x130)
 r3:00000026 r2:c081e7ac
[<c008c7e4>] (__free_percpu_irq) from [<c008c95c>] (free_percpu_irq+0x48/0x74)
 r10:00008914 r8:00000000 r7:ffffffed r6:c09356f8 r5:00000026 r4:ef11a200
[<c008c914>] (free_percpu_irq) from [<c043dd70>] (mvneta_open+0x118/0x134)
 r6:ffffffed r5:ef01e640 r4:ef01e000 r3:ef01e000
[<c043dc58>] (mvneta_open) from [<c055f5b4>] (__dev_open+0xa4/0x108)
 r7:ef01e030 r6:c06ff3d8 r5:ffff9003 r4:ef01e000
[<c055f510>] (__dev_open) from [<c055f844>] (__dev_change_flags+0x94/0x150)
 r7:00001002 r6:00000001 r5:ffff9003 r4:ef01e000
[<c055f7b0>] (__dev_change_flags) from [<c055f938>] (dev_change_flags+0x20/0x50)
 r8:00000000 r7:c09334c8 r6:00001002 r5:00000148 r4:ef01e000 r3:00008914
[<c055f918>] (dev_change_flags) from [<c05de044>] (devinet_ioctl+0x6f4/0x7e0)
 r8:00000000 r7:c09334c8 r6:00000000 r5:ee87200c r4:00000000 r3:00008914
[<c05dd950>] (devinet_ioctl) from [<c05e0168>] (inet_ioctl+0x1b8/0x1c8)
 r10:beb4499c r9:edfe4000 r8:ecf13280 r7:c096cf00 r6:beb4499c r5:eef7c240
 r4:00008914
[<c05dffb0>] (inet_ioctl) from [<c053c898>] (sock_ioctl+0x78/0x300)
[<c053c820>] (sock_ioctl) from [<c0155ecc>] (do_vfs_ioctl+0x98/0xa60)
 r7:00000011 r6:00008914 r5:00000011 r4:c01568d0
[<c0155e34>] (do_vfs_ioctl) from [<c01568d0>] (SyS_ioctl+0x3c/0x60)
 r10:00000000 r9:edfe4000 r8:beb4499c r7:00000011 r6:00008914 r5:ecf13280
 r4:ecf13280
[<c0156894>] (SyS_ioctl) from [<c000fe60>] (ret_fast_syscall+0x0/0x1c)
 r8:c0010004 r7:00000036 r6:00000011 r5:000a2978 r4:00000000 r3:00009003
---[ end trace 711f625d5b04b3a7 ]---

Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
Tested-by: Jon Nettleton <jon@solid-run.com>
Signed-off-by: David S. Miller <davem@davemloft.net>