io_uring/rsrc: fix folio unpinning

In the Linux kernel, the following vulnerability has been resolved:

io_uring/rsrc: fix folio unpinning

syzbot complains about an unmapping failure:

[ 108.070381][ T14] kernel BUG at mm/gup.c:71!
[ 108.070502][ T14] Internal error: Oops - BUG: 00000000f2000800 [#1] SMP
[ 108.123672][ T14] Hardware name: QEMU KVM Virtual Machine, BIOS edk2-20250221-8.fc42 02/21/2025
[ 108.127458][ T14] Workqueue: iou_exit io_ring_exit_work
[ 108.174205][ T14] Call trace:
[ 108.175649][ T14] sanity_check_pinned_pages+0x7cc/0x7d0 (P)
[ 108.178138][ T14] unpin_user_page+0x80/0x10c
[ 108.180189][ T14] io_release_ubuf+0x84/0xf8
[ 108.182196][ T14] io_free_rsrc_node+0x250/0x57c
[ 108.184345][ T14] io_rsrc_data_free+0x148/0x298
[ 108.186493][ T14] io_sqe_buffers_unregister+0x84/0xa0
[ 108.188991][ T14] io_ring_ctx_free+0x48/0x480
[ 108.191057][ T14] io_ring_exit_work+0x764/0x7d8
[ 108.193207][ T14] process_one_work+0x7e8/0x155c
[ 108.195431][ T14] worker_thread+0x958/0xed8
[ 108.197561][ T14] kthread+0x5fc/0x75c
[ 108.199362][ T14] ret_from_fork+0x10/0x20

We can pin a tail page of a folio, but then io_uring will try to unpin
the head page of the folio. While it should be fine in terms of keeping
the page actually alive, mm folks say it's wrong and triggers a debug
warning. Use unpin_user_folio() instead of unpin_user_page*.

[axboe: adapt to current tree, massage commit message]