video: fbdev: fsl-diu-fb: remove unneeded variable 'res'

Eliminate the following coccicheck warning:

drivers/video/fbdev/fsl-diu-fb.c:1428:5-8: Unneeded variable: "res".
Return "0" on line 1450
Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Jason Yan <yanaijie@huawei.com>
Acked-by: Gustavo A. R. Silva <gustavoars@kernel.org>
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20200910140558.1191423-1-yanaijie@huawei.com

drivers/video/fbdev/fsl-diu-fb.c

@@ -1425,7 +1425,6 @@ static int fsl_diu_open(struct fb_info *info, int user)
 static int fsl_diu_release(struct fb_info *info, int user)
 {
 	struct mfb_info *mfbi = info->par;
-	int res = 0;
 
 	spin_lock(&diu_lock);
 	mfbi->count--;
@@ -1447,7 +1446,7 @@ static int fsl_diu_release(struct fb_info *info, int user)
 	}
 
 	spin_unlock(&diu_lock);
-	return res;
+	return 0;
 }
 
 static const struct fb_ops fsl_diu_ops = {