drm: Do not leak a new reference for flink() on an existing name

The name table should only hold a single reference, so avoid leaking
additional references for secondary calls to flink().

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Eric Anholt <eric@anholt.net>
Signed-off-by: Dave Airlie <airlied@linux.ie>