Set all parameters to 0

Set all parameters to 0

Since the function dm_get_next_target() returns NULL as 'next' pointer
so it's not a 'real' error - set 0 to all parameters when NULL is
returned because of missing head.

i.e. one of use case::
do {
	next = dm_get_next_target(dmt, next, &start, &length,
				  &target_type, &params);
	size += length;
} while (next);