[CIFS] Follow on to cifsacl endian patch (__constant_cpu_to_le32 was required)

As Jeff just pointed out, __constant_cpu_to_le32 was required instead of
cpu_to_le32 in previous patch to cifsacl.c 383c5535
(Fix endian error comparing authusers when cifsacl enabled)

CC: Stable <stable@kernel.org>
Reviewed-by: Jeff Layton <jlayton@redhat.com>
CC: Shirish Pargaonkar <shirishp@us.ibm.com>
Signed-off-by: Steve French <sfrench@us.ibm.com>