ASoC: fsl_esai: Fix divisor calculation failure at lower ratio

BugLink: http://bugs.launchpad.net/bugs/1768825

commit c656941d upstream.

When the desired ratio is less than 256, the savesub (tolerance)
in the calculation would become 0. This will then fail the loop-
search immediately without reporting any errors.

But if the ratio is smaller enough, there is no need to calculate
the tolerance because PM divisor alone is enough to get the ratio.

So a simple fix could be just to set PM directly instead of going
into the loop-search.
Reported-by: Marek Vasut <marex@denx.de>
Signed-off-by: Nicolin Chen <nicoleotsuka@gmail.com>
Tested-by: Marek Vasut <marex@denx.de>
Reviewed-by: Fabio Estevam <fabio.estevam@nxp.com>
Signed-off-by: Mark Brown <broonie@kernel.org>
Cc: stable@vger.kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Juerg Haefliger <juergh@canonical.com>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>

sound/soc/fsl/fsl_esai.c

@@ -143,6 +143,13 @@ static int fsl_esai_divisor_cal(struct snd_soc_dai *dai, bool tx, u32 ratio,
 
 	psr = ratio <= 256 * maxfp ? ESAI_xCCR_xPSR_BYPASS : ESAI_xCCR_xPSR_DIV8;
 
+	/* Do not loop-search if PM (1 ~ 256) alone can serve the ratio */
+	if (ratio <= 256) {
+		pm = ratio;
+		fp = 1;
+		goto out;
+	}
+
 	/* Set the max fluctuation -- 0.1% of the max devisor */
 	savesub = (psr ? 1 : 8)  * 256 * maxfp / 1000;