drm/i915: Index min_{cdclk,voltage_level}[] with pipe

min_cdclk[] and min_voltage_level[] are supposed to be indexed
with the pipe. Fix up a few cases where we index via the crtc
index (via the atomic iterators) instead.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210204020846.2094-1-ville.syrjala@linux.intel.com
Reviewed-by: Mika Kahola <mika.kahola@intel.com>