staging: fbtft: Fix buffer overflow vulnerability

Module copies a user supplied string (module parameter) into a buffer
using strncpy() and does not check that the buffer is null terminated.

Replace call to strncpy() with call to strlcpy() ensuring that the
buffer is null terminated.

Signed-off-by: Tobin C. Harding <me@tobin.cc>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>