drivers: adc: Correct an error in Kconfig

Correct an error in ADC Kconfig. The # in the beginning of
the code lines unintentionally commented out the "if" condition.

Jira: ZEP-645

Change-Id: Ieee1bdbf4865fc39aef9a0986036fd81a75e5b58
Signed-off-by: Baohong Liu <baohong.liu@intel.com>
Signed-off-by: Qiu Peiyang <peiyangx.qiu@intel.com>