powerpc/64s/exception: Fix performance monitor virt handler

The perf virt handler uses EXCEPTION_PROLOG_2_REAL rather than _VIRT.
In practice this is okay because the _REAL variant is usable by virt
mode interrupts, but should be fixed (and is a performance win).
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20190802105709.27696-21-npiggin@gmail.com

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

@@ -750,7 +750,7 @@ END_FTR_SECTION_IFSET(CPU_FTR_CAN_NAP)
 #define __TRAMP_VIRT_OOL_MASKABLE(name, realvec, bitmask)		\
 	TRAMP_VIRT_BEGIN(tramp_virt_##name);				\
 	EXCEPTION_PROLOG_1 EXC_STD, PACA_EXGEN, 0, realvec, 0, 0, bitmask ; \
-	EXCEPTION_PROLOG_2_REAL name##_common, EXC_STD, 1
+	EXCEPTION_PROLOG_2_VIRT name##_common, EXC_STD
 
 #define EXC_VIRT_OOL_MASKABLE(name, start, size, realvec, bitmask)	\
 	__EXC_VIRT_OOL_MASKABLE(name, start, size);			\