powerpc/64s/exception: machine check adjust RFI target

The host kernel delivery case for powernv does RFI_TO_USER_OR_KERNEL,
but should just use RFI_TO_KERNEL which makes it clear this is not a
user case.

This is not a bug because RFI_TO_USER_OR_KERNEL deals with kernel
returns just fine.
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20190802105709.27696-5-npiggin@gmail.com

arch/powerpc/kernel/exceptions-64s.S

@@ -1184,7 +1184,7 @@ BEGIN_FTR_SECTION
 	 */
 	bl	machine_check_queue_event
 	MACHINE_CHECK_HANDLER_WINDUP
-	RFI_TO_USER_OR_KERNEL
+	RFI_TO_KERNEL
 FTR_SECTION_ELSE
 	/*
 	 * pSeries: Return from MC interrupt. Before that stay on emergency