ASoC: mxs-saif: fix setting master base rate

The SAIF base oversample rates are either 512*fs or 384*fs. An additional
divider exists within the SAIF to generate sub-multiples of these two base
rates if MCLK is required by the codec.

 * The sub-rates for the 512x base rate are: 256x, 128x, 64x, and 32x.
 * The sub-rates for the 384x base rate are: 192x, 96x, and 48x.

Setting the base rate depending on the modulo operation with 32 and 48
give wrong results for some mclk.

If mclk=18.432MHz both modulo operations results in 0. As testing the
result with 32 is done first, a wrong base rate of 512*fs is set instead
of the correct 384*fs.

Fix this by setting the base rate depending on the calculated sub-rate.

Signed-off-by: Jörg Krause <joerg.krause@embedded.rocks>
Signed-off-by: Mark Brown <broonie@kernel.org>