mfd: twl6040: Correct HPPLL configuration for 19.2 and 38.4 MHz mclk

When the MCLK is 19.2 or 38.4 MHz the HPPLL need to be enabled and can be
put in bypass mode.
This will fix HPPLL use on boards with 19.2MHz mclk.

Signed-off-by: Peter Ujfalusi <peter.ujfalusi@ti.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>