MdeModulePkg/Ehci: don't clear port status bits during init

MdeModulePkg/Ehci: don't clear port status bits during init

Port status bits are clear in original code, so no enumeration
takes place.
Changing this to prevent the status bits from being cleared
allows enumeration to proceed normally.

Cc: Star Zeng <star.zeng@intel.com>
Cc: Mike Turner <Michael.Turner@microsoft.com>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Mike Turner <Michael.Turner@microsoft.com>
Signed-off-by: Feng Tian <feng.tian@intel.com>
Reviewed-by: Star Zeng <star.zeng@intel.com>