mmc: rtsx: Clear SD_CLK toggle enable bit if switching voltage fail

If switching voltage fails, SD_CLK toggle enable bit should been cleared
so that SD host can control SD clock automatically.

Signed-off-by: Wei WANG <wei_wang@realsil.com.cn>
Acked-by: Chris Ball <cjb@laptop.org>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>