utils: Fix a -Wsign-compare warning in generate_hash()
utils: Fix a -Wsign-compare warning in generate_hash()

Compiling -Wextra produced the following warning

  CC    utils.o
utils.c: In function ‘generate_hash’:
utils.c:204:17: warning: comparison of integer expressions of different signedness: ‘ssize_t’ {aka ‘long int’} and ‘long unsigned int’ [-Wsign-compare]
  204 |  if (bytes_read < sizeof(buf)) {
      |                 ^

Fix this by just using ENTROPY_SIZE instead of sizeof(buf).

Signed-off-by: Andrew Clayton <02e0a999c50b1f88df7a8f5a04e1b76b35ea6a88@digital-domain.net>

ac000/fcgi_app_core,ac000/fcgi_app_core