sysutils/fluent-bit: fix build on powerpc*

In file included from /wrkdirs/usr/ports/sysutils/fluent-bit/work/fluent-bit-1.7.1/lib/monkey/deps/flb_libco/libco.c:20:
/wrkdirs/usr/ports/sysutils/fluent-bit/work/fluent-bit-1.7.1/lib/monkey/deps/flb_libco/ppc.c:282:12: error: conflicting types for 'co_create'
cothread_t co_create(unsigned int size, void (*entry_)(void)) {

^

/wrkdirs/usr/ports/sysutils/fluent-bit/work/fluent-bit-1.7.1/lib/monkey/deps/flb_libco/libco.h:19:12: note: previous declaration is here
cothread_t co_create(unsigned int, void (*)(void), size_t *);

^

1 error generated.