drm/i915: fix simple_return.cocci warnings

drivers/gpu/drm/i915/intel_ringbuffer.c:435:1-4: WARNING: end returns can be simpified

 Simplify a trivial if-return sequence.  Possibly combine with a
 preceding function call.
Generated by: scripts/coccinelle/misc/simple_return.cocci

CC: Paulo Zanoni <paulo.r.zanoni@intel.com>
Signed-off-by: Fengguang Wu <fengguang.wu@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/intel_ringbuffer.c

@@ -432,11 +432,7 @@ gen8_render_ring_flush(struct intel_engine_cs *ring,
 			return ret;
 	}
 
-	ret = gen8_emit_pipe_control(ring, flags, scratch_addr);
-	if (ret)
-		return ret;
-
-	return 0;
+	return gen8_emit_pipe_control(ring, flags, scratch_addr);
 }
 
 static void ring_write_tail(struct intel_engine_cs *ring,