ASoC: rt5677: fix rt5677 spi driver build

Create a separate module for rt5677 spi driver. Without
this patch, the build fails due to multiple defs of
'init_module' and 'cleanup_module'. module_spi_driver()
defines its own module, so it can't be part of the rt5677
module.

Signed-off-by: Ben Zhang <benzh@chromium.org>
Signed-off-by: Mark Brown <broonie@kernel.org>
diff --git a/sound/soc/codecs/rt5677-spi.c b/sound/soc/codecs/rt5677-spi.c
index 11c38f3..ef6348c 100644
--- a/sound/soc/codecs/rt5677-spi.c
+++ b/sound/soc/codecs/rt5677-spi.c
@@ -52,6 +52,7 @@
 
 	return status;
 }
+EXPORT_SYMBOL_GPL(rt5677_spi_write);
 
 /**
  * rt5677_spi_burst_write - Write data to SPI by rt5677 dsp memory address.
@@ -107,6 +108,7 @@
 
 	return 0;
 }
+EXPORT_SYMBOL_GPL(rt5677_spi_burst_write);
 
 static int rt5677_spi_probe(struct spi_device *spi)
 {