Kernel: Make Ext2FS::free_inode() return KResult, and use TRY() more

While there's no clear propagation path for errors that happen in an
inode destructor, using TRY() still makes the code a lot nicer.

Kernel/FileSystem/Ext2FileSystem.h

@@ -145,7 +145,7 @@ private:
     KResult set_block_allocation_state(BlockIndex, bool);
 
     void uncache_inode(InodeIndex);
-    void free_inode(Ext2FSInode&);
+    KResult free_inode(Ext2FSInode&);
 
     struct BlockListShape {
         unsigned direct_blocks { 0 };