ASoC: pxa-ssp: Don't use SSCR0_SerClkDiv and SSCR0_SCR

Those macros are just screwed as soon as CONFIG_PXA25x is enabled.

This patch
- changes ssp_set_scr to take an ssp_dev pointer instead of ssp_device
- adds a corresponding ssp_get_scr function.

Signed-off-by: Philipp Zabel <philipp.zabel@gmail.com>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>