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: cd9e11a8 ("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