net: dsa: microchip: remove superfluous num_ports assignment

The variable num_ports is already assigned in the init function. The
drivers individual init function already handles the different purpose
of port_cnt vs port_cnt + 1. This patch removes the extra assignment of
the variable.

Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: Michael Grzeschik <m.grzeschik@pengutronix.de>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>