Input: wdt87xx_i2c - fix format warning

This fixes the following warning:

   drivers/input/touchscreen/wdt87xx_i2c.c: In function 'wdt87xx_validate_firmware':
>> drivers/input/touchscreen/wdt87xx_i2c.c:472:4: warning: format '%zd' expects argument of type 'signed size_t', but argument 4 has type 'size_t' [-Wformat=]
       size, fw->size);

Reported-by: kbuild test robot <fengguang.wu@intel.com>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>

drivers/input/touchscreen/wdt87xx_i2c.c

@@ -468,7 +468,7 @@ static int wdt87xx_validate_firmware(struct wdt87xx_data *wdt,
 	size = get_unaligned_le32(fw->data + FW_SIZE_OFFSET);
 	if (size != fw->size) {
 		dev_err(&wdt->client->dev,
-			"fw size mismatch: expected %d, actual %zd\n",
+			"fw size mismatch: expected %d, actual %zu\n",
 			size, fw->size);
 		return -EINVAL;
 	}