RDMA/cxgb4: Annotate r2 and stag as __be32

RDMA/cxgb4: Annotate r2 and stag as __be32

Chelsio cxgb4 HW is big-endian, hence there is need to properly
annotate r2 and stag fields as __be32 and not __u32 to fix the
following sparse warnings.

  drivers/infiniband/hw/cxgb4/qp.c:614:16:
    warning: incorrect type in assignment (different base types)
      expected unsigned int [unsigned] [usertype] r2
      got restricted __be32 [usertype] <noident>
  drivers/infiniband/hw/cxgb4/qp.c:615:18:
    warning: incorrect type in assignment (different base types)
      expected unsigned int [unsigned] [usertype] stag
      got restricted __be32 [usertype] <noident>

Cc: Steve Wise <swise@opengridcomputing.com>
Signed-off-by: Leon Romanovsky <leon@kernel.org>
Reviewed-by: Steve Wise <swise@opengridcomputing.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>