ASoC: fix pxa-ssp compiling issue under mach-mmp

pxa-ssp.c uses API like cpu_is_pxa3xx(), cpu_is_pxa2xx(), which is
defined under arch-pxa architecture, and drivers under mach-mmp
can't find it. so just use ssp->type to replace that API.

Signed-off-by: Qiao Zhou <zhouqiao@marvell.com>
Acked-by: Haojian Zhuang <haojian.zhuang@gmail.com>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>