lsblk: fix, set default sort_id = -1

Introduced in 642048e4:
 $ lsblk -o SIZE /dev/loop1
lsblk: the sort column has to be between output columns.

Signed-off-by: Ruediger Meier <ruediger.meier@ga-group.nl>
Merge branch 'master' of https://github.com/rudimeier/util-linux