drm: writeback: Fix kernel doc name

During the creation of drmm_ variants for writeback connector, one
function was renamed, but not the kernel doc.

To remove the warning, use the proper name in kernel doc.

Fixes: 135d8fc ("drm: writeback: Create an helper for drm_writeback_connector initialization")
Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Closes: https://lore.kernel.org/all/20250207142201.550ce870@canb.auug.org.au/
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20250207-b4-fix-warning-v1-1-b4964beb60a3@bootlin.com
Signed-off-by: Louis Chauvet <louis.chauvet@bootlin.com>

Author: Fomys

drivers/gpu/drm/drm_writeback.c

@@ -213,7 +213,7 @@ static void delete_writeback_properties(struct drm_device *dev)
 }
 
 /**
- * drm_writeback_connector_init_with_encoder - Initialize a writeback connector with
+ * __drm_writeback_connector_init - Initialize a writeback connector with
  * a custom encoder
  *
  * @dev: DRM device