memfs_ll: fix deadlock in truncate operation

Remove redundant mutex lock acquisition in the truncate() method to
prevent deadlock. The issue occurs when memfs_setattr() already holds
the mutex lock and then calls truncate(), which attempts to acquire
the same lock again.

Signed-off-by: Long Li <leo.lilong@huawei.com>

example/memfs_ll.cc

@@ -199,7 +199,6 @@ class Inode {
 
 	void truncate(off_t size)
 	{
-		std::lock_guard<std::mutex> lock(mutex);
 		std::lock_guard<std::mutex> attr_lock(attr_mutex);
 		if (size < content.size()) {
 			content.resize(size);