fs: cifs: Drop unlikely before IS_ERR(_OR_NULL)

IS_ERR(_OR_NULL) already contain an 'unlikely' compiler flag,
so no need to do that again from its callers. Drop it.

Cc: linux-cifs@vger.kernel.org
Signed-off-by: Kefeng Wang <wangkefeng.wang@huawei.com>
Signed-off-by: Steve French <stfrench@microsoft.com>
Reviewed-by: Paulo Alcantara <palcantara@suse.de>