multipath: reset queue_if_no_path if flush failed

When flushing a map failed the 'queue_if_no_path' setting is
getting lost.

References: bnc#828868

Signed-off-by: Hannes Reinecke <hare@suse.de>
multipath: Fixup compilation warnings

The compiler complained about several minor issues.

Signed-off-by: Hannes Reinecke <hare@suse.de>