f2fs: don't call iput() from f2fs_drop_inode()

iput() calls the problematic routine, which does a ->i_count inc/dec
cycle. Undoing it with iput() recurses into the problem.

Note f2fs should not be playing games with the refcount to begin with,
but that will be handled later. Right now solve the immediate
regression.

Fixes: bc986b1 ("fs: stop accessing ->i_count directly in f2fs and gfs2")
Reported-by: kernel test robot <oliver.sang@intel.com>
Closes: https://lore.kernel.org/oe-lkp/202509301450.138b448f-lkp@intel.com
Signed-off-by: Mateusz Guzik <mjguzik@gmail.com>
Reviewed-by: Chao Yu <chao@kernel.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

Author: mjguzik

fs/f2fs/super.c

@@ -1820,7 +1820,7 @@ static int f2fs_drop_inode(struct inode *inode)
 			sb_end_intwrite(inode->i_sb);
 
 			spin_lock(&inode->i_lock);
-			iput(inode);
+			atomic_dec(&inode->i_count);
 		}
 		trace_f2fs_drop_inode(inode, 0);
 		return 0;