io_uring/register: use atomic_read/write for sq_flags migration

A previous commit changed all of the migration from the old to the new
ring for resizing to use READ/WRITE_ONCE. However, ->sq_flags is an
atomic_t, and while most archs won't complain on this, some will indeed
flag this:

io_uring/register.c:554:9: sparse: sparse: cast to non-scalar
io_uring/register.c:554:9: sparse: sparse: cast from non-scalar

Just use atomic_set/atomic_read for handling this case.

Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202501242000.A2sKqaCL-lkp@intel.com/


Fixes: 2c5aae12 ("io_uring/register: document io_register_resize_rings() shared mem usage")
Signed-off-by: Jens Axboe <axboe@kernel.dk>