drm/hisilicon: Use the same style of variable type in hibmc_drm_de

Consistently Use the same style of variable type in hibmc_drm_de.c.

Signed-off-by: Tian Tao <tiantao6@hisilicon.com>
Acked-by: Thomas Zimmermann <tzimmermann@suse.de>
Link: https://patchwork.freedesktop.org/patch/msgid/1602808711-65193-2-git-send-email-tiantao6@hisilicon.com