CVE-2026-74393: drm/syncobj: Fix memory leak in drm_syncobj_find_fence()

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

drm/syncobj: Fix memory leak in drmsyncobjfindfence()

Commit 18226ba52159 ("drm/syncobj: reject invalid flags in drmsyncobjfindfence") forgot to take into account the fact that drmsyncobjfind() takes a reference to syncobj and returns early without dropping the reference, leading to memory leaks.

Reported by: Sam Spencer <sam.spencer@arm.com>