btrfs: always return -EIOCBQUEUED after btrfs_uring_read_extent_endio

btrfs: always return -EIOCBQUEUED after btrfs_uring_read_extent_endio

If all bios finish before btrfs_encoded_read_regular_fill_pages()
returns, it calls btrfs_uring_read_extent_endio() and previously
returned the I/O status.  A negative errno then made
btrfs_uring_read_extent() unlock and free while
btrfs_uring_read_finished() did the same again.

Return -EIOCBQUEUED so only the deferred path cleans up.

Reported-by: Yue Sun <samsun1006219@gmail.com>
Closes: https://lore.kernel.org/linux-btrfs/20260630091609.3414-1-samsun1006219@gmail.com/
Suggested-by: Jens Axboe <axboe@kernel.dk>
Fixes: 34310c442e17 ("btrfs: add io_uring command for encoded reads (ENCODED_READ ioctl)")
Signed-off-by: Yang Xiuwei <yangxiuwei@kylinos.cn>
Signed-off-by: David Sterba <dsterba@suse.com>