minigbm: make drv_add_combinations return nothing

Two reasons for this:

	1) We can use drv_array for driver combinations (see next patch)
	2) It's less verbose.

BUG=chromium:764871
TEST=gbmtest passes

Change-Id: I39bea6e2e9e4c76d2ca78566926a79bdc17f11d0
Reviewed-on: https://chromium-review.googlesource.com/758148
Commit-Ready: Gurchetan Singh <gurchetansingh@chromium.org>
Tested-by: Gurchetan Singh <gurchetansingh@chromium.org>
Reviewed-by: Stéphane Marchesin <marcheu@chromium.org>
diff --git a/nouveau.c b/nouveau.c
index 4efbda2..d0f25d4 100644
--- a/nouveau.c
+++ b/nouveau.c
@@ -12,11 +12,8 @@
 
 static int nouveau_init(struct driver *drv)
 {
-	int ret;
-	ret = drv_add_combinations(drv, render_target_formats, ARRAY_SIZE(render_target_formats),
-				   &LINEAR_METADATA, BO_USE_RENDER_MASK);
-	if (ret)
-		return ret;
+	drv_add_combinations(drv, render_target_formats, ARRAY_SIZE(render_target_formats),
+			     &LINEAR_METADATA, BO_USE_RENDER_MASK);
 
 	return drv_modify_linear_combinations(drv);
 }