cifs: don't use GFP_KERNEL with GFP_NOFS

GFP_KERNEL and GFP_NOFS are mutually exclusive. If you combine them, you end up
with plain GFP_KERNEL which can deadlock in cases where you really want
GFP_NOFS.

Cc: Steve French <sfrench@samba.org>
Signed-off-by: Pekka Enberg <penberg@cs.helsinki.fi>
Signed-off-by: Steve French <sfrench@us.ibm.com>