drm/draw: fix color truncation in drm_draw_fill24

drm/draw: fix color truncation in drm_draw_fill24

The color parameter passed to drm_draw_fill24() was truncated to 16
bits, leading to an incorrect color drawn to the target iosys_map.
Fix this behavior, widening the parameter to 32 bits.

Fixes: 31fa2c1ca0b2 ("drm/panic: Move drawing functions to drm_draw")
Signed-off-by: Francesco Valla <francesco@valla.it>
Reviewed-by: Jocelyn Falempe <jfalempe@redhat.com>
Link: https://lore.kernel.org/r/20251003-drm_draw_fill24_fix-v1-1-8fb7c1c2a893@valla.it
Signed-off-by: Jocelyn Falempe <jfalempe@redhat.com>