ASoC: mediatek: mt8192: Fix build failure

A build of arm64 allmodconfig with next-20201105 fails with the error:
ERROR: modpost: "mt8192_afe_gpio_request" undefined!
ERROR: modpost: "mt8192_afe_gpio_init" undefined!

Export the symbols so that mt8192-mt6359-rt1015-rt5682.ko finds it.
Signed-off-by: Sudip Mukherjee <sudipm.mukherjee@gmail.com>
Link: https://lore.kernel.org/r/20201105124747.18383-1-sudipm.mukherjee@gmail.comSigned-off-by: Mark Brown <broonie@kernel.org>

sound/soc/mediatek/mt8192/mt8192-afe-gpio.c

@@ -160,6 +160,7 @@ int mt8192_afe_gpio_init(struct device *dev)
 
 	return 0;
 }
+EXPORT_SYMBOL(mt8192_afe_gpio_init);
 
 static int mt8192_afe_gpio_adda_dl(struct device *dev, bool enable)
 {
@@ -304,3 +305,4 @@ int mt8192_afe_gpio_request(struct device *dev, bool enable,
 
 	return 0;
 }
+EXPORT_SYMBOL(mt8192_afe_gpio_request);