ASoC: pxa: Fix module autoload for platform drivers

These platform drivers are lacking MODULE_ALIAS so module autoloading
doesn't work. Tested on corgi and poodle with kernel 4.4.

Signed-off-by: Andrea Adami <andrea.adami@gmail.com>
Signed-off-by: Mark Brown <broonie@kernel.org>

sound/soc/pxa/mmp-sspa.c

@@ -482,3 +482,4 @@ module_platform_driver(asoc_mmp_sspa_driver);
 MODULE_AUTHOR("Leo Yan <leoy@marvell.com>");
 MODULE_DESCRIPTION("MMP SSPA SoC Interface");
 MODULE_LICENSE("GPL");
+MODULE_ALIAS("platform:mmp-sspa-dai");