RDMA/bnxt_re: Make use of destroy AH sleepable flag

When in a sleepable (non-atomic) context, wait for firmware completion
instead of polling for it.

Signed-off-by: Gal Pressman <galpress@amazon.com>
Acked-by: Selvin Xavier <selvin.xavier@broadcom.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>