video: fbdev: mb862xx: remove set but not used variable 'mdr'

Fix the following gcc warning:

drivers/video/fbdev/mb862xx/mb862xxfb_accel.c:187:6: warning: variable
‘mdr’ set but not used [-Wunused-but-set-variable]
int mdr;
^~~

Reported-by: Hulk Robot <[e-mail]>
Signed-off-by: Jason Yan <[e-mail]>
Signed-off-by: Sam Ravnborg <[e-mail]>
Link: https://patchwork.freedesktop.org/patch/msgid/[e-mail]

drivers/video/fbdev/mb862xx/mb862xxfb_accel.c

···
 static void mb86290fb_imageblit(struct fb_info *info,
 				const struct fb_image *image)
 {
-	int mdr;
 	u32 *cmd = NULL;
 	void (*cmdfn) (u32 *, u16, u16, u16, u16, u16, u32, u32,
 		       const struct fb_image *, struct fb_info *) = NULL;
···
 	u16 dx = image->dx, dy = image->dy;
 	int x2, y2, vxres, vyres;
 
-	mdr = (GDC_ROP_COPY << 9);
 	x2 = image->dx + image->width;
 	y2 = image->dy + image->height;
 	vxres = info->var.xres_virtual;