powerpc/spufs: don't extend time time slice if context is not in spu_run

An spu context shouldn't get an extra tick if the time slice code
couldn't find something else to run. This means contexts that are not
within spu_run (ie, SPU_SCHED_SPU_RUN is cleared) will not receive
extra ticks while we have no other contexts waiting.
Signed-off-by: Luke Browning <lukebrowning@us.ibm.com>
Signed-off-by: Jeremy Kerr <jk@ozlabs.org>

arch/powerpc/platforms/cell/spufs/sched.c

@@ -899,7 +899,8 @@ static noinline void spusched_tick(struct spu_context *ctx)
 			spu_add_to_rq(ctx);
 	} else {
 		spu_context_nospu_trace(spusched_tick__newslice, ctx);
-		ctx->time_slice++;
+		if (!ctx->time_slice)
+			ctx->time_slice++;
 	}
 out:
 	spu_release(ctx);