OvmfPkg/SmbiosPlatformDxe: return EFI_NOT_FOUND if there is no SMBIOS data

OvmfPkg/SmbiosPlatformDxe: return EFI_NOT_FOUND if there is no SMBIOS data

According to the function-top comment, SmbiosTablePublishEntry() is
supposed to return an error code if no SMBIOS data is found, from either
GetXenSmbiosTables() or GetQemuSmbiosTables(). Currently the function
returns EFI_SUCCESS in this case however (propagated from
gBS->LocateProtocol()). Make the return code match the documentation.

(This issue is not too important, but it gets in the way of splitting the
entry point function next.)

Cc: Ard Biesheuvel <ardb+tianocore@kernel.org>
Cc: Jordan Justen <jordan.l.justen@intel.com>
Cc: Philippe Mathieu-Daudé <philmd@redhat.com>
Ref: https://bugzilla.tianocore.org/show_bug.cgi?id=2122
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Message-Id: <20210526201446.12554-38-lersek@redhat.com>
Reviewed-by: Ard Biesheuvel <ardb@kernel.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>