Software clear the MDIO interrupt before MDIO bus access, but
MAC still generate MDIO interrupt. The issue only happen on
imx6slx chip.

CPU: 0 PID: 1 Comm: swapper/0 Not tainted 3.17.0-rc1-00399-g0bcad17 #315
Backtrace:
[<800121fc>] (dump_backtrace) from [<800124e0>] (show_stack+0x18/0x1c)
 r6:8096e534 r5:8096e534 r4:00000000 r3:00000000
[<800124c8>] (show_stack) from [<806a4c60>] (dump_stack+0x8c/0xa4)
[<806a4bd4>] (dump_stack) from [<80060ab8>] (__lock_acquire+0x1814/0x1c40)
 r6:be078000 r5:be074000 r4:be03f6e4 r3:be078000
[<8005f2a4>] (__lock_acquire) from [<800616e0>] (lock_acquire+0x70/0x84)
 r10:809ada33 r9:be010600 r8:00000096 r7:00000001 r6:be074000 r5:00000000
 r4:60000193
[<80061670>] (lock_acquire) from [<806abb20>] (_raw_spin_lock_irqsave+0x40/0x54)
 r7:00000000 r6:8005a3f8 r5:00000193 r4:be03f6d4
[<806abae0>] (_raw_spin_lock_irqsave) from [<8005a3f8>] (complete+0x1c/0x4c)
 r6:80950904 r5:be03f6d0 r4:be03f6d4
[<8005a3dc>] (complete) from [<8041b4c0>] (fec_enet_interrupt+0x128/0x164)
 r6:80950904 r5:00800000 r4:be03f000 r3:00000000
[<8041b398>] (fec_enet_interrupt) from [<8006aeac>] (handle_irq_event_percpu+0x38/0x13c)
 r6:00000000 r5:be01065c r4:be399e00 r3:8041b398
[<8006ae74>] (handle_irq_event_percpu) from [<8006aff4>] (handle_irq_event+0x44/0x64)
 r10:be03f000 r9:80989fe0 r8:00000000 r7:00000096 r6:be399e00 r5:be01065c
 r4:be010600
[<8006afb0>] (handle_irq_event) from [<8006e3e8>] (handle_fasteoi_irq+0xc8/0x1bc)
 r6:8096e764 r5:be01065c r4:be010600 r3:00000000
[<8006e320>] (handle_fasteoi_irq) from [<8006a63c>] (generic_handle_irq+0x30/0x44)
 r6:be074010 r5:80945e4c r4:00000096 r3:8006e320
[<8006a60c>] (generic_handle_irq) from [<8000f218>] (handle_IRQ+0x54/0xbc)
 r4:80950d74 r3:00000180
[<8000f1c4>] (handle_IRQ) from [<800086cc>] (gic_handle_irq+0x30/0x68)
 r8:be3ab478 r7:c080e100 r6:be075bd8 r5:80950eec r4:c080e10c r3:000000a0
[<8000869c>] (gic_handle_irq) from [<80013064>] (__irq_svc+0x44/0x5c)
Signed-off-by: Fugang Duan <B38611@freescale.com>
Signed-off-by: Frank Li <Frank.Li@freescale.com>
Signed-off-by: David S. Miller <davem@davemloft.net>