Fix potential missing '\0' when wrapping to legacy

The HAL API for port name is a C++ string of arbitrary
length.
Nevertheless the legacy API name had a maximum length.
Thus when wrapping from the new to legacy, the string
was truncated but no '\0' was added.

Bug: 38184704
Test: compile
Change-Id: I482363809718281e022041c2d5042e5800c5a617
Merged-In: I482363809718281e022041c2d5042e5800c5a617
Cherry-picked from master
Signed-off-by: Kevin Rocard <krocard@google.com>