ASoC: omap-mcbsp: Correct clock muxing for CLKR/FSR signals

Remove the no longer valid check for McBSP1 regarding to signal mux
selection (on OMAP4 McBSP4 has 6 pin setup).
Only clear the srgr2, pcr0 register configuration if the requested clock
configuration will actually going to touch it. In this way we can avoid
issues if the CLKR/FSR mux has been configured after the clock selection.

We are going to check for the valid McBSP port in the
omap_mcbsp_6pin_src_mux() function based on the validity of the mux_signal
callback (which is only valid for ports having 6 pin setup).

Signed-off-by: Peter Ujfalusi <peter.ujfalusi@ti.com>
Acked-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Signed-off-by: Liam Girdwood <lrg@ti.com>
diff --git a/sound/soc/omap/mcbsp.c b/sound/soc/omap/mcbsp.c
index 95413a1..e5f4444 100644
--- a/sound/soc/omap/mcbsp.c
+++ b/sound/soc/omap/mcbsp.c
@@ -690,7 +690,9 @@
 int omap_mcbsp_6pin_src_mux(struct omap_mcbsp *mcbsp, u8 mux)
 {
 	const char *signal, *src;
-	int ret = 0;
+
+	if (mcbsp->pdata->mux_signal)
+		return -EINVAL;
 
 	switch (mux) {
 	case CLKR_SRC_CLKR:
@@ -713,10 +715,7 @@
 		return -EINVAL;
 	}
 
-	if (mcbsp->pdata->mux_signal)
-		ret = mcbsp->pdata->mux_signal(mcbsp->dev, signal, src);
-
-	return ret;
+	return mcbsp->pdata->mux_signal(mcbsp->dev, signal, src);
 }
 
 #define max_thres(m)			(mcbsp->pdata->buffer_size)