net: mvneta: Fix lacking spinlock initialization

The spinlock used by the hwbm functions must be initialized by the
network driver. This commit fixes this lack and the following erros when
lockdep is enabled:

INFO: trying to register non-static key.
the code is fine but needs lockdep annotation.
turning off the locking correctness validator.
[<c010ff80>] (unwind_backtrace) from [<c010bd08>] (show_stack+0x10/0x14)
[<c010bd08>] (show_stack) from [<c032913c>] (dump_stack+0xb4/0xe0)
[<c032913c>] (dump_stack) from [<c01670e4>] (__lock_acquire+0x1f58/0x2060)
[<c01670e4>] (__lock_acquire) from [<c0167dec>] (lock_acquire+0xa4/0xd0)
[<c0167dec>] (lock_acquire) from [<c06f6650>] (_raw_spin_lock_irqsave+0x54/0x68)
[<c06f6650>] (_raw_spin_lock_irqsave) from [<c058e830>] (hwbm_pool_add+0x1c/0xdc)
[<c058e830>] (hwbm_pool_add) from [<c043f4e8>] (mvneta_bm_pool_use+0x338/0x490)
[<c043f4e8>] (mvneta_bm_pool_use) from [<c0443198>] (mvneta_probe+0x654/0x1284)
[<c0443198>] (mvneta_probe) from [<c03b894c>] (platform_drv_probe+0x4c/0xb0)
[<c03b894c>] (platform_drv_probe) from [<c03b7158>] (driver_probe_device+0x214/0x2c0)
[<c03b7158>] (driver_probe_device) from [<c03b72c4>] (__driver_attach+0xc0/0xc4)
[<c03b72c4>] (__driver_attach) from [<c03b5440>] (bus_for_each_dev+0x68/0x9c)
[<c03b5440>] (bus_for_each_dev) from [<c03b65b8>] (bus_add_driver+0x1a0/0x218)
[<c03b65b8>] (bus_add_driver) from [<c03b79cc>] (driver_register+0x78/0xf8)
[<c03b79cc>] (driver_register) from [<c01018f4>] (do_one_initcall+0x90/0x1dc)
[<c01018f4>] (do_one_initcall) from [<c0900de4>] (kernel_init_freeable+0x15c/0x1fc)
[<c0900de4>] (kernel_init_freeable) from [<c06eed90>] (kernel_init+0x8/0x114)
[<c06eed90>] (kernel_init) from [<c0107910>] (ret_from_fork+0x14/0x24)

Fixes: baa11ebc ("net: mvneta: Use the new hwbm framework")
Reported-by: Russell King <rmk+kernel@armlinux.org.uk>
Cc: <stable@vger.kernel.org>
Signed-off-by: Gregory CLEMENT <gregory.clement@free-electrons.com>
Signed-off-by: David S. Miller <davem@davemloft.net>