freecalypso-tools: fix -Werror=format-security in get_pirelli_imei()

[Mychaela Falconia]

Hi Vadim,

Thank you for the bug report!  I just pushed a fix, although I had to
make it slightly different from your patch:

* My first thought was also to change printf() to puts() like you did,
  but puts() adds '\n' at the end, hence the static-allocated string
  would have to be changed to remove its trailing '\n'.

* Then I thought that this error msg should probably go to stderr, so
  I changed that line to:

  fputs(failmsg, stderr);

Unlike plain puts(), fputs() does not add '\n', hence we should be
good now. :-)

M~