swiotlb-xen: suppress certain init retries

Only on the 2nd of the paths leading to xen_swiotlb_init()'s "error"
label it is useful to retry the allocation; the first one did already
iterate through all possible order values.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/56477481-87da-4962-9661-5e1b277efde0@suse.com


Signed-off-by: Juergen Gross <jgross@suse.com>