fec: fix recursive locking of mii_lock

mii_discover_phy is only called by fec_enet_mii (via mip->mii_func).  So
&fep->mii_lock is already held and mii_discover_phy must not call
mii_queue which locks &fep->mii_lock, too.

This was noticed by lockdep:

	=============================================
	[ INFO: possible recursive locking detected ]
	2.6.31-rc8-00038-g37d0892 #109
	---------------------------------------------
	swapper/1 is trying to acquire lock:
	 (&fep->mii_lock){-.....}, at: [<c01569f8>] mii_queue+0x2c/0xcc

	but task is already holding lock:
	 (&fep->mii_lock){-.....}, at: [<c0156328>] fec_enet_interrupt+0x78/0x460

	other info that might help us debug this:
	2 locks held by swapper/1:
	 #0:  (rtnl_mutex){+.+.+.}, at: [<c0183534>] rtnl_lock+0x18/0x20
	 #1:  (&fep->mii_lock){-.....}, at: [<c0156328>] fec_enet_interrupt+0x78/0x460

	stack backtrace:
	Backtrace:
	[<c00226fc>] (dump_backtrace+0x0/0x108) from [<c01eac14>] (dump_stack+0x18/0x1c)
	 r6:c781d118 r5:c03e41d8 r4:00000001
	[<c01eabfc>] (dump_stack+0x0/0x1c) from [<c005bae4>] (__lock_acquire+0x1a20/0x1a88)
	[<c005a0c4>] (__lock_acquire+0x0/0x1a88) from [<c005bbac>] (lock_acquire+0x60/0x74)
	[<c005bb4c>] (lock_acquire+0x0/0x74) from [<c01edda8>] (_spin_lock_irqsave+0x54/0x68)
	 r7:60000093 r6:c01569f8 r5:c785e468 r4:00000000
	[<c01edd54>] (_spin_lock_irqsave+0x0/0x68) from [<c01569f8>] (mii_queue+0x2c/0xcc)
	 r7:c785e468 r6:c0156b24 r5:600a0000 r4:c785e000
	[<c01569cc>] (mii_queue+0x0/0xcc) from [<c0156b78>] (mii_discover_phy+0x54/0xa8)
	 r8:00000002 r7:00000032 r6:c785e000 r5:c785e360 r4:c785e000
	[<c0156b24>] (mii_discover_phy+0x0/0xa8) from [<c0156354>] (fec_enet_interrupt+0xa4/0x460)
	 r5:c785e360 r4:c077a170
	[<c01562b0>] (fec_enet_interrupt+0x0/0x460) from [<c0066674>] (handle_IRQ_event+0x48/0x120)
	[<c006662c>] (handle_IRQ_event+0x0/0x120) from [<c0068438>] (handle_level_irq+0x94/0x11c)
	...

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Cc: Greg Ungerer <gerg@uclinux.org>
Cc: Ben Hutchings <ben@decadent.org.uk>
Cc: Patrick McHardy <kaber@trash.net>
Cc: Sascha Hauer <s.hauer@pengutronix.de>
Cc: Matt Waddel <Matt.Waddel@freescale.com>
Cc: netdev@vger.kernel.org
Cc: Tim Sander <tim01@vlsi.informatik.tu-darmstadt.de>
Acked-by: Greg Ungerer <gerg@uclinux.org>
Signed-off-by: David S. Miller <davem@davemloft.net>