nvmecontrol(8): Fix typo in ns.c

Insufficient was spelled wrongly on line 537.

Event: Advanced UNIX Programming Course (Fall’23) at NTHU.
Pull Request: https://github.com/freebsd/freebsd-src/pull/997

(cherry picked from commit 69f9c5a51346b1ada4854cb4131e8a63b7dd8b46)