io_uring/uring_cmd: don't assume io_uring_cmd_data layout

io_uring/uring_cmd: don't assume io_uring_cmd_data layout

eaf72f7b414f ("io_uring/uring_cmd: cleanup struct io_uring_cmd_data
layout") removed most of the places assuming struct io_uring_cmd_data
has sqes as its first field. However, the EAGAIN case in io_uring_cmd()
still compares ioucmd->sqe to the struct io_uring_cmd_data pointer using
a void * cast. Since fa3595523d72 ("io_uring: get rid of alloc cache
init_once handling"), sqes is no longer io_uring_cmd_data's first field.
As a result, the pointers will always compare unequal and memcpy() may
be called with the same source and destination.

Replace the incorrect void * cast with the address of the sqes field.

Signed-off-by: Caleb Sander Mateos <csander@purestorage.com>
Fixes: eaf72f7b414f ("io_uring/uring_cmd: cleanup struct io_uring_cmd_data layout")
Link: https://lore.kernel.org/r/20250212204546.3751645-2-csander@purestorage.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>