drm/vram-helper: fix function names in vram helper doc

Refer to drmm_vram_helper_init() instead of the non-existent
drmm_vram_helper_alloc_mm().

Fixes: a5f23a72 ("drm/vram-helper: Managed vram helpers")
Signed-off-by: Luc Ma <luc@sietium.com>
Reviewed-by: Thomas Zimmermann <tzimmermann@suse.de>
Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Link: https://patchwork.freedesktop.org/patch/msgid/64583db2.630a0220.eb75d.8f51@mx.google.com

drivers/gpu/drm/drm_gem_vram_helper.c

@@ -45,7 +45,7 @@ static const struct drm_gem_object_funcs drm_gem_vram_object_funcs;
  * the frame's scanout buffer or the cursor image. If there's no more space
  * left in VRAM, inactive GEM objects can be moved to system memory.
  *
- * To initialize the VRAM helper library call drmm_vram_helper_alloc_mm().
+ * To initialize the VRAM helper library call drmm_vram_helper_init().
  * The function allocates and initializes an instance of &struct drm_vram_mm
  * in &struct drm_device.vram_mm . Use &DRM_GEM_VRAM_DRIVER to initialize
  * &struct drm_driver and  &DRM_VRAM_MM_FILE_OPERATIONS to initialize
@@ -73,7 +73,7 @@ static const struct drm_gem_object_funcs drm_gem_vram_object_funcs;
  *		// setup device, vram base and size
  *		// ...
  *
- *		ret = drmm_vram_helper_alloc_mm(dev, vram_base, vram_size);
+ *		ret = drmm_vram_helper_init(dev, vram_base, vram_size);
  *		if (ret)
  *			return ret;
  *		return 0;
@@ -86,7 +86,7 @@ static const struct drm_gem_object_funcs drm_gem_vram_object_funcs;
  * to userspace.
  *
  * You don't have to clean up the instance of VRAM MM.
- * drmm_vram_helper_alloc_mm() is a managed interface that installs a
+ * drmm_vram_helper_init() is a managed interface that installs a
  * clean-up handler to run during the DRM device's release.
  *
  * For drawing or scanout operations, rsp. buffer objects have to be pinned