cifs: Allow passwords which begin with a delimitor

Fixes a regression in cifs_parse_mount_options where a password
which begins with a delimitor is parsed incorrectly as being a blank
password.

Signed-off-by: Sachin Prabhu <sprabhu@redhat.com>
Acked-by: Jeff Layton <jlayton@redhat.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Steve French <sfrench@us.ibm.com>