Fix various Coverity-detected errors in nvmecontrol
This fixes several Coverity-detected errors in nvmecontrol. While in
here, a couple additional errors with shift/mask confusion that were
not diagnosed by Coverity are also fixed.
CIDs addressed:
1040299,
1040300,
1403972,
1403973,
1403985,
1403988,
1403990,
1404374,
1404427,
1404469,
1404510,
1404534,
1418118
CID
1403657 (resource leak of shared library handle) was marked
"intentional" in the Coverity scan database.
Reviewed by: vangyzen, robert.herndon_dell.com
Reviewed by: daniel.william.ryan_gmail.com (earlier version)
Reviewed by: rramsden_isilon.com (earlier version), imp
MFC after: 5 days
Sponsored by: Dell EMC Isilon
Differential Revision: https://reviews.freebsd.org/D24203