drm/amdgpu: don't add files at control minor debugfs directory

Since commit 8a357d10043c ("drm: Nerf DRM_CONTROL nodes"), a
struct drm_device's ->control member is always NULL.

In the case of CONFIG_DEBUG_FS=y, amdgpu_debugfs_add_files() accesses
->control->debugfs_root though. This results in a NULL pointer
dereference.

Fix this by omitting the drm_debugfs_create_files() call for the
control minor debugfs directory which is now non-existent anyway.

Fixes: 8a357d10043c ("drm: Nerf DRM_CONTROL nodes")
Signed-off-by: Nicolai Stange <nicstange@gmail.com>
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=98915
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Tested-by: Mike Lothian <mike@fireburn.co.uk>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/20161205203022.11671-1-nicstange@gmail.com

drivers/gpu/drm/amd/amdgpu/amdgpu_device.c

@@ -2505,9 +2505,6 @@ int amdgpu_debugfs_add_files(struct amdgpu_device *adev,
 	adev->debugfs[adev->debugfs_count].num_files = nfiles;
 	adev->debugfs_count = i;
 #if defined(CONFIG_DEBUG_FS)
-	drm_debugfs_create_files(files, nfiles,
-				 adev->ddev->control->debugfs_root,
-				 adev->ddev->control);
 	drm_debugfs_create_files(files, nfiles,
 				 adev->ddev->primary->debugfs_root,
 				 adev->ddev->primary);
@@ -2521,9 +2518,6 @@ static void amdgpu_debugfs_remove_files(struct amdgpu_device *adev)
 	unsigned i;
 
 	for (i = 0; i < adev->debugfs_count; i++) {
-		drm_debugfs_remove_files(adev->debugfs[i].files,
-					 adev->debugfs[i].num_files,
-					 adev->ddev->control);
 		drm_debugfs_remove_files(adev->debugfs[i].files,
 					 adev->debugfs[i].num_files,
 					 adev->ddev->primary);