Kernel: Rename Inode::m_lock => m_inode_lock

This makes file system code much easier to read since it was hard when
both the file system and inode locks were called "m_lock".

Kernel/FileSystem/Inode.h

@@ -108,7 +108,7 @@ protected:
     void did_modify_contents();
     void did_delete_self();
 
-    mutable Mutex m_lock { "Inode" };
+    mutable Mutex m_inode_lock { "Inode" };
 
 private:
     FileSystem& m_file_system;