Fixes gcc '-Wunused-but-set-variable' warning:

drivers/infiniband/hw/bnxt_re/ib_verbs.c: In function 'bnxt_re_create_gsi_qp':
drivers/infiniband/hw/bnxt_re/ib_verbs.c:1283:30: warning:
 variable 'dev_attr' set but not used [-Wunused-but-set-variable]

commit 8dae419f ("RDMA/bnxt_re: Refactor queue pair creation code")
involved this, but not used, so remove it.

Link: https://lore.kernel.org/r/20200227064542.91205-1-yuehaibing@huawei.comReported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>