io_uring/zcrx: fix sgtable leak on mapping failures

io_uring/zcrx: fix sgtable leak on mapping failures

In an unlikely case when io_populate_area_dma() fails, which could only
happen on a PAGE_POOL_32BIT_ARCH_WITH_64BIT_DMA machine,
io_zcrx_map_area() will have an initialised and not freed table. It was
supposed to be cleaned up in the error path, but !is_mapped prevents
that.

Fixes: 439a98b972fbb ("io_uring/zcrx: deduplicate area mapping")
Cc: stable@vger.kernel.org
Reported-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>