w1: Fix bus counting in w1_get_bus

Use uclass_first_device_check/uclass_next_device_check to correctly
count buses that fail to probe.

Fixes: d3e19cf919 ("w1: Add 1-Wire uclass")
Signed-off-by: Michal Suchanek <msuchanek@suse.de>
Reviewed-by: Simon Glass <sjg@chromium.org>
1 file changed