ASoC: ti: omap-mcbsp-st: Remove set, but unused variable 'w'

Looks like 'w' has remained unchecked since the driver's inception.

Fixes the following W=1 kernel build warning(s):

 sound/soc/ti/omap-mcbsp-st.c: In function ‘omap_mcbsp_st_chgain’:
 sound/soc/ti/omap-mcbsp-st.c:145:6: warning: variable ‘w’ set but not used [-Wunused-but-set-variable]

Peter suggested that the whole read can be removed, so that's
been done too.
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Acked-by: Peter Ujfalusi <peter.ujfalusi@ti.com>
Cc: Peter Ujfalusi <peter.ujfalusi@ti.com>
Cc: Jarkko Nikula <jarkko.nikula@bitmer.com>
Cc: Samuel Ortiz <samuel.ortiz@nokia.com>
Cc: linux-omap@vger.kernel.org
Link: https://lore.kernel.org/r/20200707190612.97799-10-pierre-louis.bossart@linux.intel.comSigned-off-by: Mark Brown <broonie@kernel.org>

sound/soc/ti/omap-mcbsp-st.c

@@ -142,11 +142,8 @@ static void omap_mcbsp_st_fir_write(struct omap_mcbsp *mcbsp, s16 *fir)
 
 static void omap_mcbsp_st_chgain(struct omap_mcbsp *mcbsp)
 {
-	u16 w;
 	struct omap_mcbsp_st_data *st_data = mcbsp->st_data;
 
-	w = MCBSP_ST_READ(mcbsp, SSELCR);
-
 	MCBSP_ST_WRITE(mcbsp, SGAINCR, ST_CH0GAIN(st_data->ch0gain) |
 		       ST_CH1GAIN(st_data->ch1gain));
 }