PeiCore: Remove assertion when failing to load PE image
EFI_PEI_LOAD_FILE_PPI is invoked by DxeIpl for loading DxeCore.
It's possible that the instance produced by PeiCore fails to load but
other instances of EFI_PEI_LOAD_FILE_PPI can load.
Signed-off-by: Ray Ni <ray.ni@intel.com> Cc: Jian J Wang <jian.j.wang@intel.com> Acked-by: Hao A Wu <hao.a.wu@intel.com> Cc: Dandan Bi <dandan.bi@intel.com> Cc: Liming Gao <gaoliming@byosoft.com.cn>