Revert "USB: xhci: Use GFP_ATOMIC under spin_lock"

This reverts commit ef821ae7.

The correct thing to do is to drop the spinlock, not change
the GFP flag here.

Thanks to Sarah for pointing out I shouldn't have taken this patch in
the first place.

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