phy: rockchip-emmc: Be tolerant to card clock of 0 in power on

It's possible that there are some reasons to turn the PHY on while the
clock is 0.  In this case we just won't wait for the DLL to lock.

This is a bit of a stopgap until we figure out exactly when we're
supposed to wait for the DLL to lock and when we're supposed to power
cycle the PHY.

Note: this patch should help with suspend/resume where the system will
try to turn the PHY back on when the clock is 0.

Signed-off-by: Douglas Anderson <dianders@chromium.org>
Reviewed-by: Kishon Vijay Abraham I <kishon@ti.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>