hwmon: (ntc_thermistor): Fix sparse warnings

Fixes the following sparse warnings:
drivers/hwmon/ntc_thermistor.c:46:31: warning:
symbol 'ncpXXwb473' was not declared. Should it be static?
drivers/hwmon/ntc_thermistor.c:82:31: warning:
symbol 'ncpXXwl333' was not declared. Should it be static?

Cc: MyungJoo Ham <myungjoo.ham@samsung.com>
Signed-off-by: Sachin Kamat <sachin.kamat@linaro.org>
Acked-by: MyungJoo Ham <myungjoo.ham@samsung.com>
Acked-by: Jean Delvare <khali@linux-fr.org>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>