drm/cma-helper: Fix drm_gem_cma_free_object()

The logic for freeing an imported buffer with a virtual address is
broken. It will free the buffer instead of unmapping the dma buf.
Fix by reversing the if ladder and first check if the buffer is imported.

Fixes: b9068cde ("drm/cma-helper: Add DRM_GEM_CMA_VMAP_DRIVER_OPS")
Cc: stable@vger.kernel.org
Reported-by: "Li, Tingqian" <tingqian.li@intel.com>
Signed-off-by: Noralf Trønnes <noralf@tronnes.org>
Reviewed-by: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190426124753.53722-1-noralf@tronnes.org

drivers/gpu/drm/drm_gem_cma_helper.c

@@ -186,13 +186,13 @@ void drm_gem_cma_free_object(struct drm_gem_object *gem_obj)
 
 	cma_obj = to_drm_gem_cma_obj(gem_obj);
 
-	if (cma_obj->vaddr) {
-		dma_free_wc(gem_obj->dev->dev, cma_obj->base.size,
-			    cma_obj->vaddr, cma_obj->paddr);
-	} else if (gem_obj->import_attach) {
+	if (gem_obj->import_attach) {
 		if (cma_obj->vaddr)
 			dma_buf_vunmap(gem_obj->import_attach->dmabuf, cma_obj->vaddr);
 		drm_prime_gem_destroy(gem_obj, cma_obj->sgt);
+	} else if (cma_obj->vaddr) {
+		dma_free_wc(gem_obj->dev->dev, cma_obj->base.size,
+			    cma_obj->vaddr, cma_obj->paddr);
 	}
 
 	drm_gem_object_release(gem_obj);