mmc: omap_hsmmc: ensure pbias configuration is always done

Go through the driver's set_power() functions rather than
calling regulator_enable/disable() directly because otherwise
pbias configuration for MMC1 is not done.

Signed-off-by: Adrian Hunter <adrian.hunter@nokia.com>
Acked-by: Balaji T K <balajitk@ti.com>
Signed-off-by: Chris Ball <cjb@laptop.org>