drm/i915: Add missing 'else' to intel_digital_port_connected()

intel_digital_port_connected() lacks one 'else'. There's no
actual harm in not having it since each branch has an unconditional
return, so it can't accidentally end up in taking two branches instead
of just the one. But let's be consistent and add the 'else' anyway.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1455201868-31527-1-git-send-email-ville.syrjala@linux.intel.com
Reviewed-by: Jani Nikula <jani.nikula@intel.com>