drm/tegra: Fix non-debugfs builds

The new debugfs registration fails to build when CONFIG_DEBUGFS is
disabled, because the drm_crtc structure is lacking a member in that
configuration:

drivers/gpu/drm/tegra/dc.c: In function 'tegra_dc_late_register':
drivers/gpu/drm/tegra/dc.c:1204:28: error: 'struct drm_crtc' has no member named 'debugfs_entry'

Without CONFIG_DEBUGFS, the rest of the function already degrades
into nothing, so we just avoid the one assignment.

Fixes: b95800ee ("drm/tegra: dc: Register debugfs in ->late_register()")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Thierry Reding <treding@nvidia.com>

drivers/gpu/drm/tegra/dc.c

@@ -1242,10 +1242,16 @@ static int tegra_dc_late_register(struct drm_crtc *crtc)
 {
 	unsigned int i, count = ARRAY_SIZE(debugfs_files);
 	struct drm_minor *minor = crtc->dev->primary;
-	struct dentry *root = crtc->debugfs_entry;
+	struct dentry *root;
 	struct tegra_dc *dc = to_tegra_dc(crtc);
 	int err;
 
+#ifdef CONFIG_DEBUG_FS
+	root = crtc->debugfs_entry;
+#else
+	root = NULL;
+#endif
+
 	dc->debugfs_files = kmemdup(debugfs_files, sizeof(debugfs_files),
 				    GFP_KERNEL);
 	if (!dc->debugfs_files)