UefiCpuPkg/RegisterCpuFeaturesLib: Set CpuFeatureEntry initial value

UefiCpuPkg/RegisterCpuFeaturesLib: Set CpuFeatureEntry initial value

CpuFeatureEntry will be set before using it. But VS2012 build reported the build
warning "potentially uninitialized local variable 'CpuFeatureEntry' used".

This fix is to set CpuFeatureEntry initial value and add ASSERT check later.

Cc: Feng Tian <feng.tian@intel.com>
Cc: Michael Kinney <michael.d.kinney@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Jeff Fan <jeff.fan@intel.com>
Reviewed-by: Feng Tian <feng.tian@intel.com>