vdev_id: Fix PHY sorting

vdev_id: Fix PHY sorting

One of our developers noticed a bug in vdev_id where we were incorrectly
sorting PHYs using alphabetical sorting (which usually works) instead
of natural sorting (-v).  For example:

	[port-0:0]# ls -d phy*
	phy-0:10  phy-0:11  phy-0:8  phy-0:9

	[port-0:0]# ls -vd phy*
	phy-0:8  phy-0:9  phy-0:10  phy-0:11

This fixes the issue.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Tony Hutter <hutter2@llnl.gov>
Closes #12699