gpu: ion: Replace strncpy with strlcpy

strncpy is unsafe because it does not guarantee
that the resultant string is NULL-terminated.

Replace strncpy with strlcpy and remove explicit
NULL-termination. Also correct allocation of
string buffer.

Change-Id: Id5075ef7b04f80e2bf828f52def329b926e9ec3f
Signed-off-by: Olav Haugan <ohaugan@codeaurora.org>