ntb_perf should not require more than one memory window per peer. This
was probably an off-by-one error.

Fixes: 5648e56d ("NTB: ntb_perf: Add full multi-port NTB API support")
Signed-off-by: NLogan Gunthorpe <logang@deltatee.com>
Acked-by: NAllen Hubbe <allenbh@gmail.com>
Tested-by: NAlexander Fomichev <fomichev.ru@gmail.com>
Signed-off-by: NJon Mason <jdmason@kudzu.us>