fix(openocd-scripts): Always use SWD

OpenOCD tried

    Info : auto-selecting first available session transport "jtag".
           To override use 'transport select <transport>'.

using a JLink debugger.  Overriding it with SWD is what I did. With the
CMSIS debugger OpenOCD you get lucky:

    Info : auto-selecting first available session transport "swd".

Hope forcing it always to SWD will make it easier for others using
different debuggers.