contrib/plugins/drcov: Fix string format

This fixes on Darwin:

  plugins/drcov.c:52:13: warning: format specifies type 'unsigned long' but the argument has type 'uint64_t' (aka 'unsigned long long') [-Wformat]
              start_code, end_code, entry, path);
              ^~~~~~~~~~
  plugins/drcov.c:52:25: warning: format specifies type 'unsigned long' but the argument has type 'uint64_t' (aka 'unsigned long long') [-Wformat]
              start_code, end_code, entry, path);
                          ^~~~~~~~
  plugins/drcov.c:52:35: warning: format specifies type 'unsigned long' but the argument has type 'uint64_t' (aka 'unsigned long long') [-Wformat]
              start_code, end_code, entry, path);
                                    ^~~~~

Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Message-ID: <20230907105004.88600-3-philmd@linaro.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>