MdeModulePkg: SmmIplEntry(): don't suppress SMM core startup failure

MdeModulePkg: SmmIplEntry(): don't suppress SMM core startup failure

When the ExecuteSmmCoreFromSmram() function fails, SmmIplEntry()
restores the SMRAM range to EFI_MEMORY_UC. However, it saves the
return value of gDS->SetMemorySpaceAttributes() in the same Status
variable that gDS->contains the return value of ExecuteSmmCoreFromSmram().

Therefore, if gDS->SetMemorySpaceAttributes() succeeds, the failure
of ExecuteSmmCoreFromSmram() is masked, and Bad Things Happen (TM).

Introduce a temporary variable just for the return value of
gDS->SetMemorySpaceAttributes().

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Feng Tian <feng.tian@intel.com>
git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@17417 6f19259b-4bc3-4df7-8a09-765794883524