USB: fsl_usb2_udc: fix recursive lock

UDC needs to release lock before calling out to gadget driver, since
it may need to reenter.  The change fixes kernel BUG observed on rt
kernel.

> kernel BUG at kernel/rtmutex.c:683!
> stopped custom tracer.
> Oops: Exception in kernel mode, sig: 5 [#1]
> PREEMPT MPC834x ITX
> NIP: c021629c LR: c0216270 CTR: 00000000
> REGS: df761d70 TRAP: 0700   Not tainted  (2.6.23.9-rt13)
> MSR: 00021032 <ME,IR,DR>  CR: 28000022  XER: 00000000
> TASK = df632080[241] 'IRQ-38' THREAD: df760000
> GPR00: 00000001 df761e20 df632080 00000000 11111111 00000000 df761e6c
> 00000000
> GPR08: df761e48 00000000 df761e50 00000000 80000000 ede5cdde 1fffd000
> 00800000
> GPR16: ffffffff 00000000 007fff00 00000040 00000000 007ffeb0 00000000
> 1fff8b08
> GPR24: 00000000 00000026 00000000 df79a320 c026b2e8 c02240bc 00009032
> df79a320
> NIP [c021629c] rt_spin_lock_slowlock+0x9c/0x200
> LR [c0216270] rt_spin_lock_slowlock+0x70/0x200
> Call Trace:
> [df761e20] [c0216270] rt_spin_lock_slowlock+0x70/0x200 (unreliable)
> [df761e90] [c0182828] fsl_ep_disable+0xcc/0x154
> [df761eb0] [c0184d30] eth_reset_config+0x88/0x1d0
> [df761ed0] [c0184ec0] eth_disconnect+0x48/0x64
> [df761ef0] [c01831a4] reset_queues+0x60/0x78
> [df761f00] [c0183b74] fsl_udc_irq+0x9b8/0xa58
> [df761f50] [c003ef30] handle_IRQ_event+0x64/0x100
> [df761f80] [c003f758] thread_simple_irq+0x6c/0xc8
> [df761fa0] [c003f888] do_irqd+0xd4/0x2e4
> [df761fd0] [c0032284] kthread+0x50/0x8c
> [df761ff0] [c000f9b4] kernel_thread+0x44/0x60

Signed-off-by: Li Yang <leoli@freescale.com>
Cc: Eugene T. Bordenkircher <Eugene_Bordenkircher@selinc.com>
Acked-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>