hwmon: (ina2xx) don't accept shunt values greater than the calibration factor

Shunt resistance values greater than the chip's calibration factor make no
sense since the actual value written to the register equals:

	<calibration factor> / <shunt>

Bail-out from ina2xx_probe() if the configured value is greater than the
calibration factor.

Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>