mfd: altera-a10sr: Make altr_a10sr_regmap_config static const

It's only used in this driver and never get modified, make it static const.
Signed-off-by: Axel Lin <axel.lin@ingics.com>
Reviewed-by: Thor Thayer <tthayer@opensource.altera.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>

drivers/mfd/altera-a10sr.c

@@ -94,7 +94,7 @@ static bool altr_a10sr_reg_volatile(struct device *dev, unsigned int reg)
 	}
 }
 
-const struct regmap_config altr_a10sr_regmap_config = {
+static const struct regmap_config altr_a10sr_regmap_config = {
 	.reg_bits = 8,
 	.val_bits = 8,