ASoC: samsung: change neo1973_audio from a global to static

sparse reports
sound/soc/samsung/neo1973_wm8753.c:347:24: warning: symbol 'neo1973_audio' was not declared. Should it be static?

neo1973_audio is only used in neo1973_wm8753.c, so it's
storage class specifier should be static.

Fixes: e26a2abc ("ASoC: samsung: neo1973: turn into platform driver")
Signed-off-by: Tom Rix <trix@redhat.com>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/20220629201811.2537853-1-trix@redhat.comSigned-off-by: Mark Brown <broonie@kernel.org>

sound/soc/samsung/neo1973_wm8753.c

@@ -344,7 +344,7 @@ static int neo1973_probe(struct platform_device *pdev)
 	return devm_snd_soc_register_card(dev, &neo1973);
 }
 
-struct platform_driver neo1973_audio = {
+static struct platform_driver neo1973_audio = {
 	.driver = {
 		.name = "neo1973-audio",
 		.pm = &snd_soc_pm_ops,