contrib/plugins/cflow: fix warning

contrib/plugins/cflow: fix warning

contrib/plugins/cflow.c: In function ‘plugin_exit’:
contrib/plugins/cflow.c:167:19: error: declaration of ‘n’ shadows a previous local [-Werror=shadow=local]
  167 |         NodeData *n = l->data;
      |                   ^
contrib/plugins/cflow.c:139:9: note: shadowed declaration is here
  139 |     int n = 0;
      |         ^

Signed-off-by: Pierrick Bouvier <pierrick.bouvier@linaro.org>
Message-Id: <20241023212812.1376972-2-pierrick.bouvier@linaro.org>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>