drm/etnaviv: NULL vs IS_ERR() buf in etnaviv_core_dump()

The etnaviv_gem_get_pages() never returns NULL.  It returns error
pointers on error.

Fixes: a8c21a54 ("drm/etnaviv: add initial etnaviv DRM driver")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Lucas Stach <l.stach@pengutronix.de>

drivers/gpu/drm/etnaviv/etnaviv_dump.c

@@ -215,7 +215,7 @@ void etnaviv_core_dump(struct etnaviv_gpu *gpu)
 		mutex_lock(&obj->lock);
 		pages = etnaviv_gem_get_pages(obj);
 		mutex_unlock(&obj->lock);
-		if (pages) {
+		if (!IS_ERR(pages)) {
 			int j;
 
 			iter.hdr->data[0] = bomap - bomap_start;