AK: Fix FreeBSD compilation for clock

FreeBSD introduced CLOCK_MONOTONIC_COARSE and CLOCK_REALTIME_COARSE.
This update fixes ladybird builds from FreeBSD 13.1

see clock_gettime(2) https://www.freebsd.org/cgi/man.cgi?query=clock_gettime&apropos=0&sektion=0&manpath=FreeBSD+13.1-RELEASE&arch=default&format=ascii

AK/Platform.h

@@ -166,7 +166,7 @@ extern "C" {
 #    define CLOCK_MONOTONIC_COARSE CLOCK_MONOTONIC
 #endif
 
-#if defined(AK_OS_BSD_GENERIC)
+#if defined(AK_OS_BSD_GENERIC) && !defined(AK_OS_FREEBSD)
 #    define CLOCK_MONOTONIC_COARSE CLOCK_MONOTONIC
 #    define CLOCK_REALTIME_COARSE CLOCK_REALTIME
 #endif