OvmfPkg QemuFwCfgLib: Fix broken IA32 Microsoft assembler code

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>
Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>

git-svn-id: https://edk2.svn.sourceforge.net/svnroot/edk2/trunk/edk2@14108 6f19259b-4bc3-4df7-8a09-765794883524
MU SOURCE COMMIT:b5e243b75f22cf87d887bc41ffcddc9b7a5f8d5c

Platforms/OvmfPkg/Library/QemuFwCfgLib/Ia32/IoLibExAsm.asm

@@ -29,7 +29,7 @@ IoReadFifo8 PROC
     mov     dx, [esp + 4]
     mov     ecx, [esp + 8]
     push    edi
-    mov     edx, [esp + 16]
+    mov     edi, [esp + 16]
 rep insb
     pop     edi
     ret