media: rkisp1: stats: remove a wrong cast to u8

hist_bins is an array of type __u32. Each entry represent
a 20 bit fixed point value as documented inline.
The cast to u8 when setting the values is wrong. Remove it.

Signed-off-by: Dafna Hirschfeld <dafna.hirschfeld@collabora.com>
Reviewed-by: Heiko Stuebner <heiko@sntech.de>
Acked-by: Helen Koike <helen.koike@collabora.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>