Add a drm_sysfs_connector_remove call when we destroy the panel to make
sure the connector node in sysfs gets deleted.

This is required for proper unload and re-load of this driver, otherwise
we will get a warning about a duplicate filename in sysfs.
Signed-off-by: Guido Martínez <guido@vanguardiasur.com.ar>
Tested-by: Darren Etheridge <detheridge@ti.com>
Cc: <stable@vger.kernel.org> #v3.9+
Signed-off-by: Dave Airlie <airlied@redhat.com>