drm: Nuke unused drm_display_info.pixel_clock

drm_display_info.pixel_clock is unused. Let's get rid of it.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190326173401.7329-1-ville.syrjala@linux.intel.com


Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>