io_uring/zcrx: remove sqe->file_index check

io_uring/zcrx: remove sqe->file_index check

sqe->file_index and sqe->zcrx_ifq_idx are aliased, so even though
io_recvzc_prep() has all necessary handling and checking for
->zcrx_ifq_idx, it's already rejected a couple of lines above.

It's not a real problem, however, as we can only have one ifq at the
moment, which index is always zero, and it returns correct error
codes to the user.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/b51acedd326d1a87bf53e33303e6fc87661a3e3f.1745141261.git.asml.silence@gmail.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>