kernel/cache: Add VMVnodeCache::Commit().

Does nothing, as Vnode (file) caches don't need to commit memory
at present.

src/system/kernel/cache/vnode_store.cpp

@@ -34,6 +34,14 @@ VMVnodeCache::Init(struct vnode* vnode, uint32 allocationFlags)
 }
 
 
+status_t
+VMVnodeCache::Commit(off_t size, int priority)
+{
+	// We don't need to commit memory.
+	return B_OK;
+}
+
+
 bool
 VMVnodeCache::HasPage(off_t offset)
 {

src/system/kernel/cache/vnode_store.h

@@ -18,6 +18,7 @@ public:
 			status_t			Init(struct vnode* vnode,
 									uint32 allocationFlags);
 
+	virtual	status_t			Commit(off_t size, int priority);
 	virtual	bool				HasPage(off_t offset);
 
 	virtual	status_t			Read(off_t offset, const generic_io_vec* vecs,