[settings] fix unreachable code warning in fastmem bool

Signed-off-by: lizzie <lizzie@eden-emu.dev>

src/common/settings.cpp

@@ -163,8 +163,9 @@ bool IsFastmemEnabled() {
     }
 #if defined(__FreeBSD__) || defined(__OpenBSD__) || defined(__sun__)
     return false;
-#endif
+#else
     return true;
+#endif
 }
 
 static bool is_nce_enabled = false;