RDMA/bnxt_re: Limit max_pkey to 16 bit value

Some FW versios return pkey values more than 0xFFFF. pkey_tbl_len of
ib_port_attr is 16bit value. So restricting max_pkeys to 0xFFFF.

Signed-off-by: Devesh Sharma <devesh.sharma@broadcom.com>
Signed-off-by: Selvin Xavier <selvin.xavier@broadcom.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>