IB/ipath: strncpy() doesn't always NUL-terminate

strlcpy() will always null terminate the string.  node_desc is not
guaranteed to be NUL-terminated so just use memcpy().

Signed-off-by: Roel Kluin <roel.kluin@gmail.com>
Signed-off-by: Roland Dreier <rolandd@cisco.com>