lsblk: follow kernel for inverse tree

lsblk: follow kernel for inverse tree

For multi-path devices kernel defines dependence between the device
and whole-list:

	$ ls /sys/block/dm-0/slaves/
	sdb

but lsblk inserts partition into the tree:

	$ lsblk -s -oNAME,KNAME /dev/dm-1
	mpatha1   dm-1
	└─mpatha  dm-0
	  └─sdb1  sdb1     <--- !
	    └─sdb sdb

Signed-off-by: Karel Zak <kzak@redhat.com>