Let device_detect_by_name detect parent devices aswell. We
separate the devname strings by colons and call device_detect()
for each component. This makes it possible for example to

detect nand0.root.ubi.root

With the above detect will be called for nand0, nand0.root, nand0.root.ubi
and nand0.root.ubi.root. The nand0.root detection step will detect the
UBI volume and attach it.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>