ASoC: update setting for pxa ssp slave mode

SCFR bit is required to be always set if pxa ssp is in slave mode. This bit
indicates clock input to SSPSCLK is only active during data transfers.

Signed-off-by: Haojian Zhuang <haojian.zhuang@marvell.com>
Acked-by: Liam Girdwood <lrg@slimlogic.co.uk>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>