trivial: atmel_lcdfb: add missing error message

When a too small framebuffer is given, the atmel_lcdfb_check_var
silently fails.
Adding an error message will save some head scratching.
Signed-off-by: Richard Genoud <richard.genoud@gmail.com>
Signed-off-by: Jean-Christophe PLAGNIOL-VILLARD <plagnioj@jcrosoft.com>

drivers/video/atmel_lcdfb.c

@@ -461,8 +461,11 @@ static int atmel_lcdfb_check_var(struct fb_var_screeninfo *var,
 	if (info->fix.smem_len) {
 		unsigned int smem_len = (var->xres_virtual * var->yres_virtual
 					 * ((var->bits_per_pixel + 7) / 8));
-		if (smem_len > info->fix.smem_len)
+		if (smem_len > info->fix.smem_len) {
+			dev_err(dev, "Frame buffer is too small (%u) for screen size (need at least %u)\n",
+				info->fix.smem_len, smem_len);
 			return -EINVAL;
+		}
 	}
 
 	/* Saturate vertical and horizontal timings at maximum values */