mfd: cros ec: spi: Use correct module license

According to the header comment in the source file the driver is
licensed under GPL v2, so update MODULE_LICENSE() to match that.
Signed-off-by: NThierry Reding <treding@nvidia.com>
Signed-off-by: NLee Jones <lee.jones@linaro.org>

drivers/mfd/cros_ec_spi.c

@@ -374,5 +374,5 @@ static struct spi_driver cros_ec_driver_spi = {
 
 module_spi_driver(cros_ec_driver_spi);
 
-MODULE_LICENSE("GPL");
+MODULE_LICENSE("GPL v2");
 MODULE_DESCRIPTION("ChromeOS EC multi function device (SPI)");