purge: fix resolve parent device task

purge: fix resolve parent device task

This is a typo caused by leftover.
It was previously written like this :
`shell: echo /dev/$(lsblk -no pkname "{{ item }}") }}")`
and has been rewritten to :
`shell: $(lsblk --nodeps -no pkname "{{ item }}") }}")`
because we are appending later the '/dev/' in the next task.

Fixes: https://bugzilla.redhat.com/show_bug.cgi?id=1540137
Signed-off-by: Guillaume Abrioux <gabrioux@redhat.com>