usb/gadget/langwell: do not hold spin_lock when sleep

usb/gadget/langwell: do not hold spin_lock when sleep

Use GFP_ATOMIC to avoid going to sleep while holding spin_lock.
Fix based on following call trace.
[  443.445677]  [<c102a8e8>] __might_sleep+0xf7/0xff
[  443.445677]  [<c10bca9b>] dma_pool_alloc+0x27/0x2ec
[  443.445677]  [<c12e4346>] ? langwell_ep_queue+0x1eb/0x25a
[  443.445677]  [<c12e4346>] ? langwell_ep_queue+0x1eb/0x25a
[  443.445677]  [<c12e3bd9>] req_to_dtd+0x37/0x10e
[  443.445677]  [<c14d08bd>] ? _raw_spin_lock_irqsave+0x35/0x3e
[  443.445677]  [<c12e4350>] langwell_ep_queue+0x1f5/0x25a

Change-Id: I6f15cf806444caaf8ddef8b899c083445eb24345
Signed-off-by: Jacob Pan <jacob.jun.pan@linux.intel.com>
Signed-off-by: Alan Cox <alan@linux.intel.com>
Signed-off-by: Dirk Brandewie <dirk.brandewie@gmail.com>