iio: magnetometer: mmc35240: Constify struct reg_default

mmc35240_reg_defaults is not modified and can be made const to allow the
compiler to put it in read-only memory.

Before:
   text    data     bss     dec     hex filename
   9759    3288     128   13175    3377 drivers/iio/magnetometer/mmc35240.o

After:
   text    data     bss     dec     hex filename
   9823    3224     128   13175    3377 drivers/iio/magnetometer/mmc35240.o
Signed-off-by: Rikard Falkeborn <rikard.falkeborn@gmail.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/iio/magnetometer/mmc35240.c

@@ -459,7 +459,7 @@ static bool mmc35240_is_volatile_reg(struct device *dev, unsigned int reg)
 	}
 }
 
-static struct reg_default mmc35240_reg_defaults[] = {
+static const struct reg_default mmc35240_reg_defaults[] = {
 	{ MMC35240_REG_CTRL0,  0x00 },
 	{ MMC35240_REG_CTRL1,  0x00 },
 };