mlxsw: spectrum: Remove mlxsw_sp_sample_receive()

The function resolves the psample sampling group from the Rx port
because this is the only form of sampling the driver currently supports.
Subsequent patches are going to add support for Tx-based and
policy-based sampling, in which case the sampling group would not be
resolved from the Rx port.

Therefore, move this code to the Rx-specific sampling listener.

Signed-off-by: Ido Schimmel <idosch@nvidia.com>
Reviewed-by: Jiri Pirko <jiri@nvidia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>