cifs: correction of unicode header files

This patch corrects a problem of compilation errors at removal of
UNIUPR_NOLOWER definition and adds include guards to cifs_unicode.h.

Signed-off-by: Igor Druzhinin <jaxbrigs@gmail.com>
Acked-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Steve French <sfrench@us.ibm.com>