Kernel: Make VirtualFileSystem::sync() static

Kernel/FileSystem/VirtualFileSystem.h

@@ -93,7 +93,7 @@ public:
 
     InodeIdentifier root_inode_id() const;
 
-    void sync();
+    static void sync();
 
     Custody& root_custody();
     KResultOr<NonnullRefPtr<Custody>> resolve_path(StringView path, Custody& base, RefPtr<Custody>* out_parent = nullptr, int options = 0, int symlink_recursion_level = 0);

Kernel/Syscalls/sync.cpp

@@ -12,7 +12,7 @@ namespace Kernel {
 KResultOr<FlatPtr> Process::sys$sync()
 {
     REQUIRE_PROMISE(stdio);
-    VirtualFileSystem::the().sync();
+    VirtualFileSystem::sync();
     return 0;
 }
 

Kernel/Tasks/SyncTask.cpp

@@ -18,7 +18,7 @@ UNMAP_AFTER_INIT void SyncTask::spawn()
     Process::create_kernel_process(syncd_thread, "SyncTask", [] {
         dbgln("SyncTask is running");
         for (;;) {
-            VirtualFileSystem::the().sync();
+            VirtualFileSystem::sync();
             (void)Thread::current()->sleep(Time::from_seconds(1));
         }
     });