net: phy: at803x: fix NULL pointer dereference on AR9331 PHY

Latest kernel will explode on the PHY interrupt config, since it depends
now on allocated priv. So, run probe to allocate priv to fix it.

 ar9331_switch ethernet.1:10 lan0 (uninitialized): PHY [!ahb!ethernet@1a000000!mdio!switch@10:00] driver [Qualcomm Atheros AR9331 built-in PHY] (irq=13)
 CPU 0 Unable to handle kernel paging request at virtual address 0000000a, epc == 8050e8a8, ra == 80504b34
         ...
 Call Trace:
 [<8050e8a8>] at803x_config_intr+0x5c/0xd0
 [<80504b34>] phy_request_interrupt+0xa8/0xd0
 [<8050289c>] phylink_bringup_phy+0x2d8/0x3ac
 [<80502b68>] phylink_fwnode_phy_connect+0x118/0x130
 [<8074d8ec>] dsa_slave_create+0x270/0x420
 [<80743b04>] dsa_port_setup+0x12c/0x148
 [<8074580c>] dsa_register_switch+0xaf0/0xcc0
 [<80511344>] ar9331_sw_probe+0x370/0x388
 [<8050cb78>] mdio_probe+0x44/0x70
 [<804df300>] really_probe+0x200/0x424
 [<804df7b4>] __driver_probe_device+0x290/0x298
 [<804df810>] driver_probe_device+0x54/0xe4
 [<804dfd50>] __device_attach_driver+0xe4/0x130
 [<804dcb00>] bus_for_each_drv+0xb4/0xd8
 [<804dfac4>] __device_attach+0x104/0x1a4
 [<804ddd24>] bus_probe_device+0x48/0xc4
 [<804deb44>] deferred_probe_work_func+0xf0/0x10c
 [<800a0ffc>] process_one_work+0x314/0x4d4
 [<800a17fc>] worker_thread+0x2a4/0x354
 [<800a9a54>] kthread+0x134/0x13c
 [<8006306c>] ret_from_kernel_thread+0x14/0x1c

Same Issue would affect some other PHYs (QCA8081, QCA9561), so fix it
too.

Fixes: 3265f421

 ("net: phy: at803x: add fiber support")
Signed-off-by: Oleksij Rempel <o.rempel@pengutronix.de>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>