drm/hisilicon: Deleted the drm_device declaration

drm_framebuffer.h already declares struct drm_device, so there's no
need to declare it in hibmc_drm_drv.h

v2:
fixed spelling errors in commit message.

v3:
rewrite the commit message.
Signed-off-by: Tian Tao <tiantao6@hisilicon.com>
Acked-by: Thomas Zimmermann <tzimmermann@suse.de>
Link: https://patchwork.freedesktop.org/patch/msgid/1601020086-43652-1-git-send-email-tiantao6@hisilicon.com

drivers/gpu/drm/hisilicon/hibmc/hibmc_drm_drv.h

@@ -22,8 +22,6 @@
 #include <drm/drm_fb_helper.h>
 #include <drm/drm_framebuffer.h>
 
-struct drm_device;
-
 struct hibmc_connector {
 	struct drm_connector base;