ftrace: Fix strncpy() use, use strlcpy() instead of strncpy()

For NUL terminated string we always need to set '\0' at the end.

Signed-off-by: Chen Gang <gang.chen@asianux.com>
Cc: rostedt@goodmis.org
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Link: http://lkml.kernel.org/r/516243B7.9020405@asianux.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>