drm/bridge: Fix references to drm_bridge_funcs in documentation

The documentation for most of the bridge atomic operations incorrectly
reference the non-atomic version when stating the operations are
optional. Fix them, and make sure that all references to bridge
operations are correctly marked with @.

Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Signed-off-by: Andrzej Hajda <a.hajda@samsung.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190821235502.15475-1-laurent.pinchart+renesas@ideasonboard.com