xhci: Fix sleeping with IRQs disabled in xhci_stop_device()

xhci_stop_device() allocates and issues stop commands for each active endpoint.
This is done with spinlock held and interrupt disabled so we can't sleep during
memory allocation. Use GFP_NOWAIT instead

Regression from commit ddba5cd0
"xhci: Use command structures when queuing commands on the command ring"
for 3.16-rc1

Fixes: ddba5cd0 ("xhci: Use command structures when queuing commands")
Reported-by: Dan Williams <dan.j.williams@intel.com>
Reported-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: Mathias Nyman <mathias.nyman@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>