MmSupervisorPkg: Core: Return status value from SaveStateRead2

[zurcher]

Description

When consumers of gEfiSmmCpuProtocolGuid are given a ReadSaveState function that calls SysCallMmReadSaveState in MmSupervisorRing3Broker, they cannot rely on the returned Status value and may proceed to use invalid data present in the Buffer argument, since the Buffer is not manipulated in non-Success paths.
This change ensures that the function interface for this protocol works as expected by protocol consumers.

• Impacts functionality?
• Impacts security?
• Breaking change?
• Includes tests?
• Includes documentation?

How This Was Tested

Exposing failure case was this function returning Success on all CPUs, not just the CPU where a Software MMI was triggered.
Verified after the change that only the intended CPU returned Success.

Integration Instructions

Likely N/A; consumers of gEfiSmmCpuProtocolGuid should review handling of the return Status in case they were expecting Success in non-success cases.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 0% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 0.52%. Comparing base (af639ca) to head (b94ade6).

Files with missing lines	Patch %	Lines
...pervisorPkg/Core/PrivilegeMgmt/SyscallDispatcher.c	0.00%	1 Missing ⚠️

Additional details and impacted files

@@          Coverage Diff          @@
##            main    #644   +/-   ##
=====================================
  Coverage   0.52%   0.52%           
=====================================
  Files        133     133           
  Lines      20101   20101           
  Branches      60      60           
=====================================
  Hits         106     106           
  Misses     19990   19990           
  Partials       5       5           

Flag	Coverage Δ
MmSupervisorPkg	0.52% <0.00%> (ø)

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