drm/i915: use the correct encoder type when comparing

  - intel_encoder->type is INTEL_OUTPUT_SOMETHING
  - drm_encoder->encoder_type is DRM_MODE_ENCODER_SOMETHING

Here we're using intel_encoder, so compare the oranges against
oranges. While at it, rename the variable to "intel_encoder" so we
keep our naming standards used everywhere.

Luckily this was not a bug because both DRM_MODE_ENCODER_DAC and
INTEL_OUTPUT_ANALOG are defined as 1. This is the only case where the
drm definition matches the intel definition.

Signed-off-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>