rdma/siw: Use proper enumerated type in map_cqe_status

clang warns several times:

drivers/infiniband/sw/siw/siw_cq.c:31:4: warning: implicit conversion
from enumeration type 'enum siw_wc_status' to different enumeration type
'enum siw_opcode' [-Wenum-conversion]
        { SIW_WC_SUCCESS, IB_WC_SUCCESS },
        ~ ^~~~~~~~~~~~~~

Fixes: b0fff731 ("rdma/siw: completion queue methods")
Link: https://github.com/ClangBuiltLinux/linux/issues/596


Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>
Reviewed-by: Jason Gunthorpe <jgg@mellanox.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>