io_uring.h: fix missing tab
io_uring.h: fix missing tab

Makes it identical to the in-kernel 5.10 version, which then makes it
easier to notice when updates are missing.

Signed-off-by: Jens Axboe <cd8c6775e60d6f67a6984377324e5290df3d5358@kernel.dk>

axboe/liburing,axboe/liburing,axboe/liburing