omap: hsmmc: fix the hsmmc driver for am3517

AM3517 don't have the register OMAP343X_CONTROL_PBIAS_LITE and the regulators
like "vmmc", so we set a noop "set_power" function for it.

Signed-off-by: Stanley.Miao <stanley.miao@windriver.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>