audio: tlv320aic26: fix PLL register configuration

The current PLL configuration code for the tlc320aic26 codec appears to assume a
hardcoded system clock of 12 MHz.  Use the clock value provided by the DAI_OPS
API for the calculation.

Tested using a MityDSP-L138 platform providing a 24.576 MHz clock.

Signed-off-by: Michael Williamson <michael.williamson@criticallink.com>
Acked-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Signed-off-by: Liam Girdwood <lrg@ti.com>