net: dsa: qca8k: fix non static symbol warning

Fixes the following sparse warning:

drivers/net/dsa/qca8k.c:259:22: warning:
 symbol 'qca8k_regmap_config' was not declared. Should it be static?
Signed-off-by: Wei Yongjun <weiyongjun1@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/dsa/qca8k.c

@@ -256,7 +256,7 @@ static struct regmap_access_table qca8k_readable_table = {
 	.n_yes_ranges = ARRAY_SIZE(qca8k_readable_ranges),
 };
 
-struct regmap_config qca8k_regmap_config = {
+static struct regmap_config qca8k_regmap_config = {
 	.reg_bits = 16,
 	.val_bits = 32,
 	.reg_stride = 4,