phy: rockchip-emmc: emmc_phy_init() always return 0

rockchip_emmc_phy_init() return variable is not set with the error value
if clk_get() failed. 'emmcclk' is optional, thus use clk_get_optional()
and if the return value != NULL make error processing and set the
return code accordingly.

Fixes: 52c0624a phy: rockchip-emmc: Set phyctrl_frqsel based on card clock
Signed-off-by: Chris Ruehl <chris.ruehl@gtsys.com.hk>
Reviewed-by: Douglas Anderson <dianders@chromium.org>
Link: https://lore.kernel.org/r/20201210080454.17379-1-chris.ruehl@gtsys.com.hk


Signed-off-by: Vinod Koul <vkoul@kernel.org>