x86/EFI: fix runtime call status for compat mode Dom0

The top two bits (indicating error/warning classification) need to
remain the top two bits.

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>

--- a/xen/arch/x86/efi/runtime.c
+++ b/xen/arch/x86/efi/runtime.c
@@ -531,7 +531,7 @@ int efi_runtime_call(struct xenpf_efi_ru
 #ifndef COMPAT
     op->status = status;
 #else
-    op->status = (status & 0x3fffffff) | (status >> 62);
+    op->status = (status & 0x3fffffff) | ((status >> 32) & 0xc0000000);
 #endif
 
     return rc;