drm/v3d: Fix potential memory leak in the timestamp extension

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

drm/v3d: Fix potential memory leak in the timestamp extension

If fetching of userspace memory fails during the main loop, all drm sync

objs looked up until that point will be leaked because of the missing

drm_syncobj_put.

Fix it by exporting and using a common cleanup helper.

(cherry picked from commit 753ce4fea62182c77e1691ab4f9022008f25b62e)