Always initialize fd to 0 in open_dev().

Sponsored by:	Intel
Reviewed by:	carl
MFC after:	3 days
Define constants for the lengths of the serial number, model number
and firmware revision in the controller's identify structure.

Also modify consumers of these fields to ensure they only use the
specified number of bytes for their respective fields.

Sponsored by:	Intel
Reviewed by:	carl
MFC after:	3 days