ASoC: nau8540: remove redundant variable osrate

Variable osrate is being assigned but is never used hence it is
redundant and can be removed.

Cleans up clang warning:
warning: variable 'osrate' set but not used [-Wunused-but-set-variable]
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Mark Brown <broonie@kernel.org>

sound/soc/codecs/nau8540.c

@@ -362,11 +362,8 @@ static const struct snd_soc_dapm_route nau8540_dapm_routes[] = {
 
 static int nau8540_clock_check(struct nau8540 *nau8540, int rate, int osr)
 {
-	int osrate;
-
 	if (osr >= ARRAY_SIZE(osr_adc_sel))
 		return -EINVAL;
-	osrate = osr_adc_sel[osr].osr;
 
 	if (rate * osr > CLK_ADC_MAX) {
 		dev_err(nau8540->dev, "exceed the maximum frequency of CLK_ADC\n");