fbdev: fsl-diu: remove redundant null check on cmap

The null check on &info->cmap is redundant since cmap is a struct
inside fb_info and can never be null, so the check is always true.
We may remove it.

Signed-off-by: Wen Yang <wen.yang99@zte.com.cn>
Acked-by: Timur Tabi <timur@kernel.org>
Cc: zhong.weidong@zte.com.cn
Signed-off-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>