cmd/internal/obj/ppc64: fix ppc64 build

Apply mask fix from 527b478e to ppc64.

Change-Id: Iac62228f0f04fa8b138e21d82786026158267aaf
Reviewed-on: https://go-review.googlesource.com/6582Reviewed-by: Rob Pike <r@golang.org>

src/cmd/internal/obj/ppc64/asm9.go

@@ -905,17 +905,18 @@ func buildop(ctxt *obj.Link) {
 	}
 	sort.Sort(ocmp(optab[:n]))
 	for i := 0; i < n; i++ {
-		r0 := optab[i].as & obj.AMask
+		r := optab[i].as
+		r0 := r & obj.AMask
 		oprange[r0].start = optab[i:]
-		for optab[i].as&obj.AMask == r0 {
+		for optab[i].as == r {
 			i++
 		}
 		oprange[r0].stop = optab[i:]
 		i--
 
-		switch r0 {
+		switch r {
 		default:
-			ctxt.Diag("unknown op in build: %v", obj.Aconv(int(optab[i].as)))
+			ctxt.Diag("unknown op in build: %v", obj.Aconv(int(r)))
 			log.Fatalf("bad code")
 
 		case ADCBF: /* unary indexed: op (b+a); op (b) */