ksmbd: missing check for NULL in convert_to_nt_pathname()

The kmalloc() does not have a NULL check.  This code can be re-written
slightly cleaner to just use the kstrdup().

Fixes: 265fd199 ("ksmbd: use LOOKUP_BENEATH to prevent the out of share access")
Signed-off-by: NDan Carpenter <dan.carpenter@oracle.com>
Acked-by: NNamjae Jeon <linkinjeon@kernel.org>
Acked-by: NHyunchul Lee <hyc.lee@gmail.com>
Signed-off-by: NSteve French <stfrench@microsoft.com>

fs/ksmbd/misc.c

@@ -162,17 +162,14 @@ char *convert_to_nt_pathname(char *filename)
 {
 	char *ab_pathname;
 
-	if (strlen(filename) == 0) {
-		ab_pathname = kmalloc(2, GFP_KERNEL);
-		ab_pathname[0] = '\\';
-		ab_pathname[1] = '\0';
-	} else {
-		ab_pathname = kstrdup(filename, GFP_KERNEL);
-		if (!ab_pathname)
-			return NULL;
+	if (strlen(filename) == 0)
+		filename = "\\";
 
-		ksmbd_conv_path_to_windows(ab_pathname);
-	}
+	ab_pathname = kstrdup(filename, GFP_KERNEL);
+	if (!ab_pathname)
+		return NULL;
+
+	ksmbd_conv_path_to_windows(ab_pathname);
 	return ab_pathname;
 }