blockd: restore device_move semantics

blockd: restore device_move semantics

Before commit 4963db4 block device were only removed and re-added in
case of device_move() returning a non-zero value. Commit 4963db4 then
(supposedly) accidentally inverted that logic and also (probably to
work-around the problems resulting from the now inverted logic) limited
this behavior to autofs mounts, leaving the autofs codepath in a semi-
broken state.
Restore the original semantics as of before commit 4963db4 to fully
restore functionality for autofs mounts.

Fixes: 4963db4 ("blockd: use uloop_process for calling /sbin/hotplug-call mount")
Signed-off-by: Daniel Golle <daniel@makrotopia.org>