drm/i915: Silence a sparse warning

drivers/gpu/drm/i915/i915_debugfs.c:2136:3: warning: symbol
'i915_debugfs_files' was not declared. Should it be static?
Signed-off-by: NVille Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_debugfs.c

@@ -2130,7 +2130,7 @@ static struct drm_info_list i915_debugfs_list[] = {
 };
 #define I915_DEBUGFS_ENTRIES ARRAY_SIZE(i915_debugfs_list)
 
-struct i915_debugfs_files {
+static struct i915_debugfs_files {
 	const char *name;
 	const struct file_operations *fops;
 } i915_debugfs_files[] = {