Fix parameter reversal potentially causing buffer overrun.

Two arguments were reversed in calls to cam_strvis() in
nvme_da.c. This was found by a Coverity scan of this code within Dell
(Isilon). These are also marked in the FreeBSD Coverity scan as CIDs
1400526 & 1400531.

Submitted by: robert.herndon@dell.com
Reviewed by: vangyzen@, imp@
MFC after: 3 days
Sponsored by: Dell EMC Isilon
Differential Revision: https://reviews.freebsd.org/D24117