drm/radeon/kms: drop lock in return path of radeon_fence_count_emitted.

Silly bad return path.

Reported-and-Tested-by: Mikko Vinni
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
CC: stable@vger.kernel.org
Signed-off-by: Dave Airlie <airlied@redhat.com>