drm/writeback: Fix the "overview" section of the doc

Fix the bullet list declaration in the overview section.
Signed-off-by: Boris Brezillon <boris.brezillon@bootlin.com>
Reported-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Fixes: 935774cd ("drm: Add writeback connector type")
Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20180703174046.22396-1-boris.brezillon@bootlin.com

drivers/gpu/drm/drm_writeback.c

@@ -22,10 +22,13 @@
  * Writeback connectors are used to expose hardware which can write the output
  * from a CRTC to a memory buffer. They are used and act similarly to other
  * types of connectors, with some important differences:
- *  - Writeback connectors don't provide a way to output visually to the user.
- *  - Writeback connectors should always report as "disconnected" (so that
- *    clients which don't understand them will ignore them).
- *  - Writeback connectors don't have EDID.
+ *
+ * * Writeback connectors don't provide a way to output visually to the user.
+ *
+ * * Writeback connectors should always report as "disconnected" (so that
+ *   clients which don't understand them will ignore them).
+ *
+ * * Writeback connectors don't have EDID.
  *
  * A framebuffer may only be attached to a writeback connector when the
  * connector is attached to a CRTC. The WRITEBACK_FB_ID property which sets the