drm/kmb/dsi: convert to of_drm_find_and_get_bridge()

drm/kmb/dsi: 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.

This driver has global variables for the DSI host and DSI device, and code
to allocate them on probe but no code to free them when on remove. So it
does not at all support removal, and not even multiple instances. For this
reason putting the reference would be pointless here.

Reviewed-by: Louis Chauvet <louis.chauvet@bootlin.com>
Reviewed-by: Linus Walleij <linusw@kernel.org>
Link: https://patch.msgid.link/20260402-drm-bridge-alloc-getput-drm_of_find_bridge-4-v4-2-421781c8c061@bootlin.com
Signed-off-by: Luca Ceresoli <luca.ceresoli@bootlin.com>