smb: client: fix warning in cifs_match_super()

Fix potential dereference of ERR_PTR @tlink as reported by kernel test
robot

  fs/smb/client/connect.c:2775 cifs_match_super() error: 'tlink'
  dereferencing possible ERR_PTR()

Link: https://lore.kernel.org/all/[email protected]/
Signed-off-by: Paulo Alcantara (SUSE) <[email protected]>
Signed-off-by: Steve French <[email protected]>

Author: Paulo Alcantara

fs/smb/client/connect.c

@@ -2767,8 +2767,9 @@ cifs_match_super(struct super_block *sb, void *data)
 	}
 
 	tlink = cifs_get_tlink(cifs_sb_master_tlink(cifs_sb));
-	if (tlink == NULL) {
-		/* can not match superblock if tlink were ever null */
+	if (IS_ERR_OR_NULL(tlink)) {
+		pr_warn_once("%s: skip super matching due to bad tlink(%p)\n",
+			     __func__, tlink);
 		spin_unlock(&cifs_tcp_ses_lock);
 		return 0;
 	}