MdeModulePkg/SdMmcPciHcDxe Fix eMMC HS400 switch sequence

MdeModulePkg/SdMmcPciHcDxe Fix eMMC HS400 switch sequence

REF: https://bugzilla.tianocore.org/show_bug.cgi?id=1140

In eMMC HS400 switch sequence flow eMMC driver attempted
to execute SEND_STATUS just after switching bus timing to high
speed and before downgrading clock frequency to 52MHz. Since link
was at that time in incorrect state SEND_STATUS was failing which
made driver think switch to HS400 failed.
This change makes driver always change clock frequency after
switching bus timing and before executing SEND_STATUS.

Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Albecki Mateusz <mateusz.albecki@intel.com>
Reviewed-by: Hao Wu <hao.a.wu@intel.com>