mpi3mr: Check for copyin errors in mpi3mr_map_data_buffer_dma()

A failed copyin will cause the driver to use the contents of
uninitialized buffers instead, which is unlikely to be the behaviour
that we want. Check for errors.

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

Reviewed by: imp
MFC after: 1 week
Differential Revision: https://reviews.freebsd.org/D43098