ASoC: Add missed MODULE_LICENSE("GPL") for imx-pcm-fiq

This driver can be built as module and the file header indicates that
the driver is published under the GPL.
Thus add MODULE_LICENSE("GPL") for it.
Signed-off-by: Axel Lin <axel.lin@gmail.com>
Acked-by: Sascha Hauer <s.hauer@pengutronix.de>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>

sound/soc/imx/imx-pcm-fiq.c

@@ -332,3 +332,5 @@ static struct platform_driver imx_pcm_driver = {
 };
 
 module_platform_driver(imx_pcm_driver);
+
+MODULE_LICENSE("GPL");