x86: drop register reload from INT80 malicious MSI guard

None of the restored registers are actually of interest to the
subsequent code (as opposed to the similar construct on the compat
mode hypercall path).

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>

xen/arch/x86/x86_64/entry.S

@@ -286,7 +286,6 @@ ENTRY(int80_direct_trap)
 UNLIKELY_START(ne, msi_check)
         movl  $0x80,%edi
         call  check_for_unexpected_msi
-        LOAD_C_CLOBBERED
 UNLIKELY_END(msi_check)
 
         GET_CURRENT(%rbx)