cmd/9l: fix ppc64le build

The conversion accidentally dropped the +4 here.

Change-Id: Ic6181a759565c261bc1b084317f693ae249fd036
Reviewed-on: https://go-review.googlesource.com/6451Reviewed-by: Russ Cox <rsc@golang.org>

src/cmd/9l/asm.go

@@ -154,7 +154,7 @@ func gentext() {
 			// Restore TOC after bl.  The compiler put a
 			// nop here for us to overwrite.
 			o1 = 0xe8410018 // ld r2,24(r1)
-			ld.Ctxt.Arch.ByteOrder.PutUint32(s.P[r.Off:], o1)
+			ld.Ctxt.Arch.ByteOrder.PutUint32(s.P[r.Off+4:], o1)
 		}
 	}
 }