fbdev: imxfb: warn about invalid left/right margin

Warn about invalid var->left_margin or var->right_margin. Their values
are read from the device tree.

We store var->left_margin-3 and var->right_margin-1 in register
fields. These fields should be >= 0.

Fixes: 7e8549bc ("imxfb: Fix margin settings")
Signed-off-by: Martin Kaiser <martin@kaiser.cx>
Signed-off-by: Helge Deller <deller@gmx.de>

drivers/video/fbdev/imxfb.c

@@ -613,10 +613,10 @@ static int imxfb_activate_var(struct fb_var_screeninfo *var, struct fb_info *inf
 	if (var->hsync_len < 1    || var->hsync_len > 64)
 		printk(KERN_ERR "%s: invalid hsync_len %d\n",
 			info->fix.id, var->hsync_len);
-	if (var->left_margin > 255)
+	if (var->left_margin < 3  || var->left_margin > 255)
 		printk(KERN_ERR "%s: invalid left_margin %d\n",
 			info->fix.id, var->left_margin);
-	if (var->right_margin > 255)
+	if (var->right_margin < 1 || var->right_margin > 255)
 		printk(KERN_ERR "%s: invalid right_margin %d\n",
 			info->fix.id, var->right_margin);
 	if (var->yres < 1 || var->yres > ymax_mask)