drm/gma500: fix repeated words in comments

Delete the redundant word 'for'.

Signed-off-by: Jilin Yuan <yuanjilin@cdjrlc.com>
Signed-off-by: Patrik Jakobsson <patrik.r.jakobsson@gmail.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220907113927.35305-1-yuanjilin@cdjrlc.com