easylogo: avoid buffer overrun

Building easylogo with `HOST_TOOLS_ALL=y make tools` results in a build
warning due to a possible buffer overrun:

tools/easylogo/easylogo.c:453:4: note: ‘sprintf’ output between 7 and
262 bytes into a destination of size 256
    sprintf (str, "%s, 0x%02x", app, *dataptr++);
    ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Truncate the output to fit into the destination buffer.

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>