Fix unused variable warning in acpica's nsaccess.c

With clang 15, the following -Werror warning is produced:

sys/contrib/dev/acpica/components/namespace/nsaccess.c:452:29: error: variable 'NumCarats' set but not used [-Werror,-Wunused-but-set-variable]
    UINT32                  NumCarats;
                            ^

Here, 'NumCarats' is a variable that is only used when debugging. Since
acpica is contributed code, suppress the warning with a compile flag.

MFC after: 3 days