platform/chrome: cros_ec_dev - fix Unknown escape '%' warning

Fix the following sparse warning:

    drivers/platform/chrome/cros_ec_dev.c:64:45: sparse: Unknown escape '%'
Reported-by: NDan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: NOlof Johansson <olofj@chromium.org>
Reviewed-by: NGwendal Grignou <gwendal@chromium.org>
Signed-off-by: NJavier Martinez Canillas <javier.martinez@collabora.co.uk>
Signed-off-by: NOlof Johansson <olof@lixom.net>

drivers/platform/chrome/cros_ec_dev.c

@@ -61,7 +61,7 @@ static int ec_get_version(struct cros_ec_device *ec, char *str, int maxlen)
 	if (resp->current_image >= ARRAY_SIZE(current_image_name))
 		resp->current_image = 3; /* invalid */
 
-	snprintf(str, maxlen, "%s\n%s\n%s\n\%s\n", CROS_EC_DEV_VERSION,
+	snprintf(str, maxlen, "%s\n%s\n%s\n%s\n", CROS_EC_DEV_VERSION,
 		 resp->version_string_ro, resp->version_string_rw,
 		 current_image_name[resp->current_image]);