Fix missing braces in cifs_revalidate()

Fix missing braces introduced during commit
cea21805.  Though setting wbrc to 0
keeps this from causing real bug, this should have been there.

Acked-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Suresh Jayaraman <sjayaraman@suse.de>
Signed-off-by: Steve French <sfrench@us.ibm.com>