cifs: simple stats should always be enabled

CONFIG_CIFS_STATS should always be enabled as Pavel recently
noted.  Simple statistics are not a significant performance hit,
and removing the ifdef simplifies the code slightly.

Signed-off-by: Steve French <stfrench@microsoft.com>
Reviewed-by: Ronnie Sahlberg <lsahlber@redhat.com>
Reviewed-by: Pavel Shilovsky <pshilov@microsoft.com>