phy: rockchip-emmc: Minor code cleanup in rockchip_emmc_phy_power_on/off()

There's no reason to store the return value of rockchip_emmc_phy_power()
in a variable nor to check it.  Just return it.

Signed-off-by: Douglas Anderson <dianders@chromium.org>
Acked-by: Kishon Vijay Abraham I <kishon@ti.com>
Reviewed-by: Shawn Lin <shawn.lin@rock-chips.com>
Tested-by: Heiko Stuebner <heiko@sntech.de>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>