USB: xhci: Use GFP_ATOMIC under spin_lock

coccinelle check scripts/coccinelle/locks/call_kern.cocci found that
in drivers/usb/host/xhci.c an allocation with GFP_KERNEL is done
with locks held:

xhci_resume
  spin_lock_irq(xhci->lock)
    xhci_setup_msix
      kmalloc(GFP_KERNEL)

Change it to GFP_ATOMIC.

Signed-off-by: David Sterba <dsterba@suse.cz>
CC: Sarah Sharp <sarah.a.sharp@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>