[dev.power64] runtime: fix out-of-date comment in panic

LGTM=bradfitz
R=rsc, bradfitz
CC=golang-codereviews
https://golang.org/cl/162500043

src/runtime/panic.c

@@ -69,7 +69,7 @@ runtime·recovery_m(G *gp)
 	// each call to deferproc.
 	// (The pc we're returning to does pop pop
 	// before it tests the return value.)
-	// On the arm there are 2 saved LRs mixed in too.
+	// On the arm and power there are 2 saved LRs mixed in too.
 	if(thechar == '5' || thechar == '9')
 		gp->sched.sp = (uintptr)argp - 4*sizeof(uintptr);
 	else