vhost-user-blk: Improve error reporting in realize

vhost-user-blk: Improve error reporting in realize

Now that vhost_user_blk_connect() is not called from an event handler
any more, but directly from vhost_user_blk_device_realize(), we can
actually make use of Error again instead of calling error_report() in
the inner function and setting a more generic and therefore less useful
error message in realize() itself.

With Error, the callers are responsible for adding context if necessary
(such as the "-device" option the error refers to). Additional prefixes
are redundant and better omitted.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Acked-by: Raphael Norwitz <raphael.norwitz@nutanix.com>
Message-Id: <20210429171316.162022-4-kwolf@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>