powerpc/64s/exception: Fix DAR load for handle_page_fault error case

This buglet goes back to before the 64/32 arch merge, but it does not
seem to have had practical consequences because bad_page_fault does
not use the 2nd argument, but rather regs->dar/nip.
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20190802105709.27696-18-npiggin@gmail.com

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

@@ -2335,7 +2335,7 @@ handle_page_fault:
 	bl	save_nvgprs
 	mr	r5,r3
 	addi	r3,r1,STACK_FRAME_OVERHEAD
-	lwz	r4,_DAR(r1)
+	ld	r4,_DAR(r1)
 	bl	bad_page_fault
 	b	ret_from_except