drm/etnaviv: fix DMA direction handling for cached RW buffers

The dma sync operation needs to be done with DMA_BIDIRECTIONAL when
the BO is prepared for both read and write operations.

Fixes: a8c21a5 ("drm/etnaviv: add initial etnaviv DRM driver")
Signed-off-by: Lucas Stach <l.stach@pengutronix.de>
Reviewed-by: Philipp Zabel <p.zabel@pengutronix.de>
Reviewed-by: Christian Gmeiner <cgmeiner@igalia.com>

drivers/gpu/drm/etnaviv/etnaviv_gem.c

@@ -355,9 +355,11 @@ static void *etnaviv_gem_vmap_impl(struct etnaviv_gem_object *obj)
 
 static inline enum dma_data_direction etnaviv_op_to_dma_dir(u32 op)
 {
-	if (op & ETNA_PREP_READ)
+	op &= ETNA_PREP_READ | ETNA_PREP_WRITE;
+
+	if (op == ETNA_PREP_READ)
 		return DMA_FROM_DEVICE;
-	else if (op & ETNA_PREP_WRITE)
+	else if (op == ETNA_PREP_WRITE)
 		return DMA_TO_DEVICE;
 	else
 		return DMA_BIDIRECTIONAL;