tests: adc: corrects Infineon HPPASS ADC overlay channel addresses

Corrects the addressess used in the Infineon HPPASS SAR ADC overlays to
correctly use hex formatting  for channel numbers >= 10.

Assisted-by: Github Copilot:claude-opus-4.6
Signed-off-by: John Batch <john.batch@infineon.com>

Author: jsbatch

tests/drivers/adc/adc_api/boards/kit_psc3m5_evk.overlay

@@ -34,7 +34,7 @@
 		zephyr,resolution = <12>;
 	};
 
-	channel@12 {
+	channel@c {
 		reg = <12>;
 		zephyr,acquisition-time = <ADC_ACQ_TIME_DEFAULT>;
 		zephyr,gain = "ADC_GAIN_1";

tests/drivers/adc/adc_error_cases/boards/kit_psc3m5_evk.overlay

@@ -34,7 +34,7 @@
 		zephyr,resolution = <12>;
 	};
 
-	channel@12 {
+	channel@c {
 		reg = <12>;
 		zephyr,acquisition-time = <ADC_ACQ_TIME_DEFAULT>;
 		zephyr,gain = "ADC_GAIN_1";