swiotlb-xen: limit init retries

Due to the use of max(1024, ...) there's no point retrying (and issuing
bogus log messages) when the number of slabs is already no larger than
this minimum value.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>

Link: https://lore.kernel.org/r/984fa426-2b7b-4b77-5ce8-766619575b7f@suse.com


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