drm/i915: Fix HW readout for crtc_clock in HDMI mode

drm/i915: Fix HW readout for crtc_clock in HDMI mode

The conversion during HDMI HW readout from port_clock to crtc_clock was
missed when HDMI 10bpc support was added, so fix that.

v2:
- Unscrew the non-HDMI case.

Fixes: 199fce1a663f ("drm/i915/icl: Add 10-bit support for hdmi")
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=109593
Cc: Radhakrishna Sripada <radhakrishna.sripada@intel.com>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Imre Deak <imre.deak@intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190808162547.7009-1-imre.deak@intel.com
(cherry picked from commit 2969a78aead38b49e80c821a5c683544ab16160d)
Signed-off-by: Jani Nikula <jani.nikula@intel.com>