MdeModulePkg: XhciDxe: Prevent illegal memory access in XhcSetHsee

MdeModulePkg: XhciDxe: Prevent illegal memory access in XhcSetHsee

REF: https://bugzilla.tianocore.org/show_bug.cgi?id=1206

Newly added XhcSetHsee() routine reads 4 bytes into
a UINT16 variable causing issues on PCIE and NonDiscoverable
Xhci controllers. Fix that.

Cc: Ruiyu Ni <ruiyu.ni@intel.com>
Cc: Fei1 Wang <fei1.wang@intel.com>
Cc: Star Zeng <star.zeng@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Marcin Wojtas <mw@semihalf.com>
Reviewed-by: Star Zeng <star.zeng@intel.com>