doc: Replace dm_dump_all() with dm_dump_tree()

Replace dm_dump_all() with dm_dump_tree() in driver model documentation,
to reflect changes introduced in commit 14528704 ("dm: core: Rename
dm_dump_all()").

Fixes: 14528704 ("dm: core: Rename dm_dump_all()")
Signed-off-by: Dylan Corrales <deathcamel58@gmail.com>
Reviewed-by: Mattijs Korpershoek <mkorpershoek@baylibre.com>
Reivewed-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>