iomap: allocate s_dio_done_wq for async reads as well

iomap: allocate s_dio_done_wq for async reads as well

Since commit 222f2c7c6d14 ("iomap: always run error completions in user
context"), read error completions are deferred to s_dio_done_wq.  This
means the workqueue also needs to be allocated for async reads.

Fixes: 222f2c7c6d14 ("iomap: always run error completions in user context")
Reported-by: syzbot+a2b9a4ed0d61b1efb3f5@syzkaller.appspotmail.com
Signed-off-by: Christoph Hellwig <hch@lst.de>
Link: https://patch.msgid.link/20251124140013.902853-1-hch@lst.de
Tested-by: syzbot+a2b9a4ed0d61b1efb3f5@syzkaller.appspotmail.com
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Christian Brauner <brauner@kernel.org>