apparmor: fix memory leak on buffer on error exit path

Currently on the error exit path the allocated buffer is not free'd
causing a memory leak. Fix this by kfree'ing it.

Detected by CoverityScan, CID#1466876 ("Resource leaks")

Fixes: 1180b4c757aa ("apparmor: fix dangling symlinks to policy rawdata after replacement")
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: John Johansen <john.johansen@canonical.com>

security/apparmor/apparmorfs.c

@@ -1497,8 +1497,10 @@ static char *gen_symlink_name(int depth, const char *dirname, const char *fname)
 	}
 
 	error = snprintf(s, size, "raw_data/%s/%s", dirname, fname);
-	if (error >= size || error < 0)
+	if (error >= size || error < 0) {
+		kfree(buffer);
 		return ERR_PTR(-ENAMETOOLONG);
+	}
 
 	return buffer;
 }