WARN if the incoming drm_display_mode has an illegal aspect ratio
when converting it to a user mode. This should never happen unless
the driver made a mistake and put an invalid value into the aspect
ratio.

Cc: Ilia Mirkin <imirkin@alum.mit.edu>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190620142639.17518-4-ville.syrjala@linux.intel.comReviewed-by: Alex Deucher <alexander.deucher@amd.com>