drm/i915: use cpu_transcoder for TRANS_DDI_FUNC_CTL

... inside haswell_get_pipe_config. Because there's one TRANS_DDI_FUNC_CTL
register per CPU transcoder, not per pipe. This solves "unclaimed register"
messages when booting with eDP only and using the i915.disable_power_well=1.

Also fix a comment and remove an useless empty line.

The error messages were caused by:

  commit 88adfff1
  Author: Daniel Vetter <daniel.vetter@ffwll.ch>
  Date:   Thu Mar 28 10:42:01 2013 +0100
      drm/i915: hw readout support for ->has_pch_encoders

Signed-off-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Reviewed-by: Damien Lespiau <damien.lespiau@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>