btrfs: move pr_info into device_list_add

Commit 60999ca4 ("btrfs: make device scan less noisy")
adds return value 1 to device_list_add(), so that parent function can
call pr_info only when new device is added. Move the pr_info() part
into device_list_add() so that this function can be kept simple.

Signed-off-by: Anand Jain <anand.jain@oracle.com>
Reviewed-by: Josef Bacik <jbacik@fb.com>
Signed-off-by: David Sterba <dsterba@suse.com>