drm/i915: fix intel_crtc_clock_get pipe reads after "cleanup cleanup"

drm/i915: fix intel_crtc_clock_get pipe reads after "cleanup cleanup"

Despite the fixes in 8fd39b56ab768 (drm/i915: fix per-pipe reads after
"cleanup"), we missed one neighbouring read that was mistakenly replaced
with the reg value in ddc7796 (drm/i915: cleanup per-pipe reg usage).
This was preventing us from correctly determining the mode the BIOS left
the panel in for machines that neither have an OpRegion nor access to
the VBT, (e.g. the EeePC 700).

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Jesse Barnes <jbarnes@virtuousgeek.org>
Cc: stable@kernel.org
Reviewed-by: Jesse Barnes <jbarnes@virtuousgeek.org>
Signed-off-by: Keith Packard <keithp@keithp.com>