staging: r8188eu: overflow in rtw_p2p_get_go_device_address()

The go_devadd_str[] array is two characters too small to hold the
address so we corrupt memory.

I've changed the user space API slightly and I don't have a way to test
if this breaks anything.  In the original code we truncated away the
last digit of the address and the NUL terminator so it was already a bit
broken.

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Acked-by: Larry Finger <Larry.Finger@lwfinger.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>