btrfs-progs: don't fall back to recursive /dev scan

btrfs-progs: don't fall back to recursive /dev scan

If we didn't find what we are looking for in /proc/partitions,
we're not going to find it by scanning every node under /dev, either.

But that's just what btrfs_scan_for_fsid() does.

Remove that fallback; at that point btrfs_scan_for_fsid() just calls
scan_for_btrfs(), so remove the wrapper & call it directly.

Side note: so, these paths always use /proc/partitions, not libblkid.
Userspace-intiated scans default to libblkid.  I presume this is
part of the design, and intentional?  Anyway, not changing it now!

Signed-off-by: Eric Sandeen <sandeen@redhat.com>
Reviewed-by: Anand Jain <anand.jain@oracle.com>
Signed-off-by: David Sterba <dsterba@suse.cz>