Fix format security warning in newer GCC

[neheb]

In OpenWrt, -Werror=format-string is passed, making this fail compilation.

printf style functions are meant to work with format strings anyway.

[codecov-io]

Codecov Report

Merging #161 into master will decrease coverage by 0.02%.
The diff coverage is 0%.

@@            Coverage Diff             @@
##           master     #161      +/-   ##
==========================================
- Coverage   38.14%   38.12%   -0.03%     
==========================================
  Files          23       23              
  Lines        9959     9959              
  Branches     1948     1948              
==========================================
- Hits         3799     3797       -2     
- Misses       5216     5217       +1     
- Partials      944      945       +1

Impacted Files	Coverage Δ
src/io.c	45.47% <0%> (ø)	⬆️
src/session_server_ssh.c	24.31% <0%> (-0.13%)	⬇️
src/session_server_tls.c	28.24% <0%> (-0.11%)	⬇️

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[michalvasko]

Hi,
okay, no problem.

Regards,
Michal