mmc: host: omap_hsmmc: remove unnecessary pbias set_voltage

Remove the unnecessary pbias regulator_set_voltage done after
pbias regulator_disable in omap_hsmmc_set_power.

Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>
Reviewed-by: Roger Quadros <rogerq@ti.com>
Tested-by: Tony Lindgren <tony@atomide.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>