cifs: missing null check for newinode pointer

in cifs_do_create we check if newinode is valid before referencing it
but are missing the check in one place in fs/cifs/dir.c

Addresses-Coverity: 1357292 ("Dereference after null check")
Acked-by: Sachin Prabhu <sprabhu@redhat.com>
Signed-off-by: Steve French <stfrench@microsoft.com>