sanitize cifs_umount() prototype

a) superblock argument is unused
b) it always returns 0

Acked-by: Pavel Shilovsky <piastryyy@gmail.com>
Reviewed-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/fs/cifs/cifsfs.c b/fs/cifs/cifsfs.c
index 61c7aa8..2af14d4 100644
--- a/fs/cifs/cifsfs.c
+++ b/fs/cifs/cifsfs.c
@@ -172,7 +172,7 @@
 	if (inode)
 		iput(inode);
 
-	cifs_umount(sb, cifs_sb);
+	cifs_umount(cifs_sb);
 	return rc;
 }
 
@@ -189,9 +189,7 @@
 		return;
 	}
 
-	rc = cifs_umount(sb, cifs_sb);
-	if (rc)
-		cERROR(1, "cifs_umount failed with return code %d", rc);
+	cifs_umount(cifs_sb);
 }
 
 static void cifs_kill_sb(struct super_block *sb)