net: dsa: ksz: Remove dead code and fix warnings

net: dsa: ksz: Remove dead code and fix warnings

Remove ksz_port_cleanup(), which is unused. Add missing include
"ksz_common.h", which fixes the following warning when built with
make ... W=1

drivers/net/dsa/microchip/ksz_common.c:23:6: warning: no previous prototype for ‘...’ [-Wmissing-prototypes]

Note that the order of the headers cannot be swapped, as that would
trigger missing forward declaration errors, which would indicate the
way forward is to merge the two headers into one.

Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Andrew Lunn <andrew@lunn.ch>
Cc: David S. Miller <davem@davemloft.net>
Cc: Florian Fainelli <f.fainelli@gmail.com>
Cc: Tristram Ha <Tristram.Ha@microchip.com>
Cc: Vivien Didelot <vivien.didelot@gmail.com>
Cc: Woojung Huh <woojung.huh@microchip.com>
Signed-off-by: David S. Miller <davem@davemloft.net>