mlxsw: spectrum_buffers: Rename "pool" to "pr" in initialization

Be consintent with rest of the registers (pm, cm) and use "pr" here.

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