IB/mlx4: Avoid implicit enumerated type conversion

Clang warns when one enumerated type is implicitly converted to another.

drivers/infiniband/hw/mlx4/mad.c:1811:41: warning: implicit conversion
from enumeration type 'enum mlx4_ib_qp_flags' to different enumeration
type 'enum ib_qp_create_flags' [-Wenum-conversion]
                qp_init_attr.init_attr.create_flags = MLX4_IB_SRIOV_TUNNEL_QP;
                                                    ~ ^~~~~~~~~~~~~~~~~~~~~~~

drivers/infiniband/hw/mlx4/mad.c:1819:41: warning: implicit conversion
from enumeration type 'enum mlx4_ib_qp_flags' to different enumeration
type 'enum ib_qp_create_flags' [-Wenum-conversion]
                qp_init_attr.init_attr.create_flags = MLX4_IB_SRIOV_SQP;
                                                    ~ ^~~~~~~~~~~~~~~~~

The type mlx4_ib_qp_flags explicitly provides supplemental values to the
type ib_qp_create_flags. Make that clear to Clang by changing the
create_flags type to u32.

Reported-by: Nick Desaulniers <ndesaulniers@google.com>
Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>