mlxsw: spectrum_buffers: Further reduce pool size on Spectrum-2

In commit e891ce1d ("mlxsw: spectrum_buffers: Reduce pool size on
Spectrum-2"), pool size was reduced to mitigate a problem in port buffer
usage of ports split four ways. It turns out that this work around does not
solve the issue, and a further reduction is required.

Thus reduce the size of pool 0 by another 2.7 MiB, and round down to the
whole number of cells.

Fixes: e891ce1d

 ("mlxsw: spectrum_buffers: Reduce pool size on Spectrum-2")
Signed-off-by: Petr Machata <petrm@mellanox.com>
Signed-off-by: Ido Schimmel <idosch@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>