drm/panic: Fix kmsg text drawing rectangle

The rectangle height was larger than the screen size. This has no
real impact.

Reviewed-by: Javier Martinez Canillas <javierm@redhat.com>
Link: https://lore.kernel.org/r/20251009122955.562888-5-jfalempe@redhat.com


Signed-off-by: Jocelyn Falempe <jfalempe@redhat.com>