drm: renesas: rz-du: rzg2l_du_encoder: convert to of_drm_find_and_get_bridge()

drm: renesas: rz-du: rzg2l_du_encoder: convert to of_drm_find_and_get_bridge()

of_drm_find_bridge() is deprecated. Move to its replacement
of_drm_find_and_get_bridge() which gets a bridge reference, and ensure it
is put when done.

This is made somewhat simpler by the fact that 'bridge' is a local
variable.

However we need to handle both branches of the main if().

In the 'else' case, just switch to of_drm_find_and_get_bridge() to ensure
the bridge is not freed while in use in the function tail
(drm_bridge_attach() mainly).

In the 'then' case, devm_drm_panel_bridge_add_typed() already increments
the refcount using devres which ties the bridge allocation lifetime to the
device lifetime, so we would not need to do anything. However to have the
same behaviour in both branches take an additional reference here, so that
the bridge needs to be put whichever branch is taken without more
complicated logic.

Reviewed-by: Biju Das <biju.das.jz@bp.renesas.com>
Tested-by: Biju Das <biju.das.jz@bp.renesas.com>
Reviewed-by: Linus Walleij <linusw@kernel.org>
Reviewed-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Reviewed-by: Louis Chauvet <louis.chauvet@bootlin.com>
Link: https://patch.msgid.link/20260409-drm-bridge-alloc-getput-drm_of_find_bridge-4-v5-1-d7381c07788a@bootlin.com
Signed-off-by: Luca Ceresoli <luca.ceresoli@bootlin.com>