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: Dan Carpenter <dan.carpenter@oracle.com>
Acked-by: Namjae Jeon <linkinjeon@kernel.org>
Acked-by: Hyunchul Lee <hyc.lee@gmail.com>
Signed-off-by: Steve 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 {
+	if (strlen(filename) == 0)
+		filename = "\\";
+
 	ab_pathname = kstrdup(filename, GFP_KERNEL);
 	if (!ab_pathname)
 		return NULL;
 
 	ksmbd_conv_path_to_windows(ab_pathname);
-	}
 	return ab_pathname;
 }