mlxsw: spectrum_buffers: Switch function arguments

In the call path:

mlxsw_sp_hdroom_bufs_reset_sizes()
    mlxsw_sp_hdroom_int_buf_size_get()
        ->int_buf_size_get()

The 'speed' and 'mtu' arguments were mistakenly switched twice. The two
bugs thus canceled each other.

Clean this up by switching the arguments in both call sites, so that
they are passed in the right order.

Found during manual code inspection.

Signed-off-by: Danielle Ratson <danieller@nvidia.com>
Reviewed-by: Petr Machata <petrm@nvidia.com>
Signed-off-by: Ido Schimmel <idosch@nvidia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>