Lookup called during network boot (network root filesystem
for diskless workstation) has case where nd is null in
lookup. This patch fixes that in cifs_lookup.
(Shirish noted that 2.6.30 and 2.6.31 stable need the same check)
Signed-off-by: Shirish Pargaonkar <shirishp@us.ibm.com> Acked-by: Jeff Layton <jlayton@redhat.com> Tested-by: Vladimir Stavrinov <vs@inist.ru> CC: Stable <stable@kernel.org> Signed-off-by: Steve French <sfrench@us.ibm.com>