io_uring: don't unconditionally set plug->nowait = true

This causes all the bios to be submitted with REQ_NOWAIT, which can be
problematic on either btrfs or on file systems that otherwise use a mix
of block devices where only some of them support it.

For now, just remove the setting of plug->nowait = true.

Reported-by: Dan Melnic <dmm@fb.com>
Reported-by: Brian Foster <bfoster@redhat.com>
Fixes: b63534c4 ("io_uring: re-issue block requests that failed because of resources")
Signed-off-by: Jens Axboe <axboe@kernel.dk>