OvmfPkg: Use PcdOvmfWorkAreaBase instead of PcdSevEsWorkAreaBase

OvmfPkg: Use PcdOvmfWorkAreaBase instead of PcdSevEsWorkAreaBase

It is an typo error that HobList pointer should be stored at
PcdOvmfWorkAreaBase, not PcdSevEsWorkAreaBase.

Cc: Erdem Aktas <erdemaktas@google.com>
Cc: Gerd Hoffmann <kraxel@redhat.com>
Cc: James Bottomley <jejb@linux.ibm.com>
Cc: Jiewen Yao <jiewen.yao@intel.com>
Cc: Tom Lendacky <thomas.lendacky@amd.com>
Signed-off-by: Min Xu <min.m.xu@intel.com>
Reviewed-by: Jiewen Yao <jiewen.yao@intel.com>