block: don't return -EINVAL for not found names in devt_from_devname

block: don't return -EINVAL for not found names in devt_from_devname

When we didn't find a device and didn't guess it might be a partition,
it might still show up later, so don't disable rootwait for it by
returning -EINVAL.

Fixes: 079caa35f786 ("init: clear root_wait on all invalid root= strings")
Reported-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20230622150644.600327-1-hch@lst.de
Signed-off-by: Jens Axboe <axboe@kernel.dk>