usb-mtp: change default to success for usb_mtp_update_object

Commit c5ead51f90 (usb-mtp: return incomplete transfer on a lstat
failure) checks if lstat succeeded when updating attributes of a
file. However, it also changed behavior to return an error by
default. This is incorrect because for smaller file sizes, Qemu
will attempt to write the file in one go and there won't be
an object for it.

Fixes: c5ead51f90
Signed-off-by: Bandan Das <bsd@redhat.com>
Message-id: jpgwojv9pwv.fsf@linux.bootlegged.copy
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>

hw/usb/dev-mtp.c

@@ -1587,7 +1587,7 @@ done:
 
 static int usb_mtp_update_object(MTPObject *parent, char *name)
 {
-    int ret = -1;
+    int ret = 0;
 
     MTPObject *o =
         usb_mtp_object_lookup_name(parent, name, strlen(name));