drm/i915: rename AVI InfoFrame field 'PR' to 'YQ_CN_PR'

To keep the consistency with the other fields.

Signed-off-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Reviewed-by: Adam Jackson <ajax@redhat.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>