io_uring/zcrx: use correct mmap off constants

zcrx was using IORING_OFF_PBUF_SHIFT during first iterations, but there
is now a separate constant it should use. Both are 16 so it doesn't
change anything, but improve it for the future.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://patch.msgid.link/fe16ebe9ba4048a7e12f9b3b50880bd175b1ce03.1774780198.git.asml.silence@gmail.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

Author: isilence

io_uring/zcrx.c

@@ -386,7 +386,7 @@ static int io_allocate_rbuf_ring(struct io_ring_ctx *ctx,
 		return -EINVAL;
 
 	mmap_offset = IORING_MAP_OFF_ZCRX_REGION;
-	mmap_offset += (u64)id << IORING_OFF_PBUF_SHIFT;
+	mmap_offset += (u64)id << IORING_OFF_ZCRX_SHIFT;
 
 	ret = io_create_region(ctx, &ifq->rq_region, rd, mmap_offset);
 	if (ret < 0)