drm_hwcomposer: vsyncworker: Fix deadlock on exit path

vsyncworker::Routine assumes that when -EINTR is returned by
WaitForSignalOrExitLocked the lock as been released, which is not
true, so it hangs if a vsyncworker is never enabled and Exit is

Fixed by releasing lock in vsynworker::Routine on all code paths.

Signed-off-by: Alexandru Gheorghe <alexandru-cosmin.gheorghe@arm.com>
2 jobs for fix_vsyncworker_deadlock in 39 seconds (queued for 4 minutes and 14 seconds)