Do not increment PC for OPCDEC

This will already have been done by QEMU.

Fixes: https://bugs.launchpad.net/bugs/1810545
Signed-off-by: Richard Henderson <rth@twiddle.net>
diff --git a/pal.S b/pal.S
index 1781c4b..71a9397 100644
--- a/pal.S
+++ b/pal.S
@@ -291,10 +291,9 @@
 Pal_OpcDec:
 	mfpr	p0, qemu_ps
 	mfpr	p6, qemu_exc_addr
-	addq	p6, 4, p1		// increment past the faulting insn
 	blbs	p6, MchkBugCheck
 
-	STACK_FRAME p0, p1, p2, 1
+	STACK_FRAME p0, p6, p2, 1
 
 	mfpr	p0, ptEntIF
 	mfpr	$gp, ptKgp