drm/i915: sdvo: add i2c sysfs symlink to the connector's directory

This is the same what we do for DP connectors, so make things more
consistent.

Signed-off-by: Imre Deak <imre.deak@intel.com>
Reviewed-by: Antti Koskipää <antti.koskipaa@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>