ASoC: mxs: Fix mxs-saif timeout

On a mx28evk board the following errors happens on mxs-sgtl5000 probe:

[    0.660000] saif0_clk_set_rate: divider writing timeout
[    0.670000] mxs-sgtl5000: probe of mxs-sgtl5000.0 failed with error -110
[    0.670000] ALSA device list:
[    0.680000]   No soundcards found.

This timeout happens because clk_set_rate will result in writing to the DIV bits
of register HW_CLKCTRL_SAIF0 with the saif clock gated (CLKGATE bit set to one).

MX28 Reference states the following about CLKGATE:

"The DIV field can change ONLY when this clock gate bit field is low."

So call clk_prepare_enable prior to clk_set_rate to fix this problem.

After this change the mxs-saif driver can be correctly probed and audio is functional.
Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>

sound/soc/mxs/mxs-saif.c

@@ -124,6 +124,8 @@ static int mxs_saif_set_clk(struct mxs_saif *saif,
 	 *
 	 * If MCLK is not used, we just set saif clk to 512*fs.
 	 */
+	clk_prepare_enable(master_saif->clk);
+
 	if (master_saif->mclk_in_use) {
 		if (mclk % 32 == 0) {
 			scr &= ~BM_SAIF_CTRL_BITCLK_BASE_RATE;
@@ -133,6 +135,7 @@ static int mxs_saif_set_clk(struct mxs_saif *saif,
 			ret = clk_set_rate(master_saif->clk, 384 * rate);
 		} else {
 			/* SAIF MCLK should be either 32x or 48x */
+			clk_disable_unprepare(master_saif->clk);
 			return -EINVAL;
 		}
 	} else {
@@ -140,6 +143,8 @@ static int mxs_saif_set_clk(struct mxs_saif *saif,
 		scr &= ~BM_SAIF_CTRL_BITCLK_BASE_RATE;
 	}
 
+	clk_disable_unprepare(master_saif->clk);
+
 	if (ret)
 		return ret;