bnxt: Handle errors from copyout() in ioctl handlers

This is in preparation for annotating copyin() and related functions
with __result_use_check.

MFC after: 2 weeks
Differential Revision: https://reviews.freebsd.org/D43178

(cherry picked from commit 243e3ab3d34ada9da4f202f8cab90da2d6c49e5e)