iomap: always run error completions in user context

iomap: always run error completions in user context

At least zonefs expects error completions to be able to sleep.  Because
error completions aren't performance critical, just defer them to workqueue
context unconditionally.

Fixes: 8dcc1a9d90c1 ("fs: New zonefs file system")
Signed-off-by: Christoph Hellwig <hch@lst.de>
Link: https://patch.msgid.link/20251113170633.1453259-3-hch@lst.de
Reviewed-by: Jan Kara <jack@suse.cz>
Reviewed-by: Chaitanya Kulkarni <kch@nvidia.com>
Signed-off-by: Christian Brauner <brauner@kernel.org>