ARM: mx28evk: set a initial clock rate for saif

Signed-off-by: Dong Aisheng <b29396@freescale.com>
Acked-by: Marek Vasut <marek.vasut@gmail.com>
Cc: Sascha Hauer <s.hauer@pengutronix.de>
Cc: Wolfram Sang <w.sang@pengutronix.de>
Cc: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Cc: Mark Brown <broonie@opensource.wolfsonmicro.com>
Cc: Liam Girdwood <lrg@ti.com>
Signed-off-by: Shawn Guo <shawn.guo@linaro.org>