mfd: stpmic1: Make stpmic1_regmap_config static

Fix sparse warning:

drivers/mfd/stpmic1.c:62:28: warning:
 symbol 'stpmic1_regmap_config' was not declared. Should it be static?
Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>

drivers/mfd/stpmic1.c

@@ -59,7 +59,7 @@ static const struct regmap_access_table stpmic1_volatile_table = {
 	.n_yes_ranges = ARRAY_SIZE(stpmic1_volatile_ranges),
 };
 
-const struct regmap_config stpmic1_regmap_config = {
+static const struct regmap_config stpmic1_regmap_config = {
 	.reg_bits = 8,
 	.val_bits = 8,
 	.cache_type = REGCACHE_RBTREE,