ASoC: rt5665: make local symbol rt5665_i2c_driver static

Fixes the following sparse warnings:

sound/soc/codecs/rt5665.c:4928:19: warning:
symbol 'rt5665_i2c_driver' was not declared. Should it be static?
Signed-off-by: Wei Yongjun <weiyongjun1@huawei.com>
Signed-off-by: Mark Brown <broonie@kernel.org>

sound/soc/codecs/rt5665.c

@@ -4929,7 +4929,7 @@ static struct acpi_device_id rt5665_acpi_match[] = {
 MODULE_DEVICE_TABLE(acpi, rt5665_acpi_match);
 #endif
 
-struct i2c_driver rt5665_i2c_driver = {
+static struct i2c_driver rt5665_i2c_driver = {
 	.driver = {
 		.name = "rt5665",
 		.of_match_table = of_match_ptr(rt5665_of_match),