drm/i915/dsi: Dont forget to clean up the connector on error (v2)

If an error is encountered during the DSI initialization setup, the
drm connector object also needs to be cleaned up along with the encoder.
The error can happen due to a missing mode in the VBT or for other
reasons.

v2: Rephrase the commit message to make it more clear.

Cc: Jani Nikula <jani.nikula@intel.com>
Cc: Vandita Kulkarni <vandita.kulkarni@intel.com>
Signed-off-by: Vivek Kasireddy <vivek.kasireddy@intel.com>
Reviewed-by: José Roberto de Souza <jose.souza@intel.com>
Signed-off-by: José Roberto de Souza <jose.souza@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200522202630.7604-1-vivek.kasireddy@intel.com