ASoC: kirkwood-i2s: fix a compilation warning

In the function kirkwood_set_rate, when the rate cannot be satisfied
by the internal nor by an external clock, the clock source in undefined:

 warning: ‘clks_ctrl’ may be used uninitialized in this function

The ALSA subsystem should never gives such a rate because:
- the rates with the internal clock are limited to 44.1, 48 and 96 kHz
  as specified by the kirkwood_i2s_dai structure,
- the other rates are proposed in the structure kirkwood_i2s_dai_extclk
  only when the external clock is present.

In case of programming error (bad rate for internal clock and no
external clock), the function will simply cause a backtrace.
Signed-off-by: NJean-Francois Moine <moinejf@free.fr>
Signed-off-by: NMark Brown <broonie@linaro.org>

sound/soc/kirkwood/kirkwood-i2s.c

@@ -102,14 +102,16 @@ static void kirkwood_set_rate(struct snd_soc_dai *dai,
 	uint32_t clks_ctrl;
 
 	if (rate == 44100 || rate == 48000 || rate == 96000) {
-		/* use internal dco for supported rates */
+		/* use internal dco for the supported rates
+		 * defined in kirkwood_i2s_dai */
 		dev_dbg(dai->dev, "%s: dco set rate = %lu\n",
 			__func__, rate);
 		kirkwood_set_dco(priv->io, rate);
 
 		clks_ctrl = KIRKWOOD_MCLK_SOURCE_DCO;
-	} else if (!IS_ERR(priv->extclk)) {
-		/* use optional external clk for other rates */
+	} else {
+		/* use the external clock for the other rates
+		 * defined in kirkwood_i2s_dai_extclk */
 		dev_dbg(dai->dev, "%s: extclk set rate = %lu -> %lu\n",
 			__func__, rate, 256 * rate);
 		clk_set_rate(priv->extclk, 256 * rate);