hwmon: (s3c-hwmon) Depend on S3C_ADC

This way we don't need to modify Kconfig every time a new SoC comes along to
make this driver support it. Also fix some typos while I'm at it.

Signed-off-by: Maurus Cuelenaere <mcuelenaere@gmail.com>
Reviewed-by: Guenter Roeck <guenter.roeck@ericsson.com>
Signed-off-by: Jean Delvare <khali@linux-fr.org>