drm/v3d: Validate passed in drm syncobj handles in the timestamp extension

In the Linux kernel, the following vulnerability has been resolved:

drm/v3d: Validate passed in drm syncobj handles in the timestamp extension

If userspace provides an unknown or invalid handle anywhere in the handle

array the rest of the driver will not handle that well.

Fix it by checking handle was looked up successfully or otherwise fail the

extension by jumping into the existing unwind.

(cherry picked from commit 8d1276d1b8f738c3afe1457d4dff5cc66fc848a3)