dm mpath: fix NULL pointer dereference when path parameters missing

multipath_ctr() forgets to return an error after detecting
missing path parameters.  Fix this.

Signed-off-by: Patrick LoPresti <lopresti@gmail.com>
Cc: stable@kernel.org
Signed-off-by: Alasdair G Kergon <agk@redhat.com>
1 file changed