gpio: pca953x: Make symbol 'pca953x_i2c_regmap' static

Fixes the following sparse warning:

drivers/gpio/gpio-pca953x.c:292:28: warning:
 symbol 'pca953x_i2c_regmap' was not declared. Should it be static?

Fixes: 4942723276 ("gpio: pca953x: Perform basic regmap conversion")
Signed-off-by: Wei Yongjun <weiyongjun1@huawei.com>
Reviewed-by: Marek Vasut <marex@denx.de>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

drivers/gpio/gpio-pca953x.c

@@ -289,7 +289,7 @@ static bool pca953x_volatile_register(struct device *dev, unsigned int reg)
 	return pca953x_check_register(chip, reg, bank);
 }
 
-const struct regmap_config pca953x_i2c_regmap = {
+static const struct regmap_config pca953x_i2c_regmap = {
 	.reg_bits = 8,
 	.val_bits = 8,