net: dsa: sja1105: Make static_config_check_memory_size static

Fix sparse warning:

drivers/net/dsa/sja1105/sja1105_static_config.c:446:1: warning:
 symbol 'static_config_check_memory_size' was not declared. Should it be static?

Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Acked-by: Vladimir Oltean <olteanv@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>