mlxsw: spectrum_qdisc: Fix 64-bit division error in mlxsw_sp_qdisc_tbf_rate_kbps

When building arm32 allmodconfig:

ERROR: "__aeabi_uldivmod"
[drivers/net/ethernet/mellanox/mlxsw/mlxsw_spectrum.ko] undefined!

rate_bytes_ps has type u64, we need to use a 64-bit division helper to
avoid a build error.

Fixes: a44f58c4 ("mlxsw: spectrum_qdisc: Support offloading of TBF Qdisc")
Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>
Reviewed-by: Ido Schimmel <idosch@mellanox.com>
Tested-by: Ido Schimmel <idosch@mellanox.com>
Acked-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>