stm32h7: adc: DUAL_PAD: fix definitions for GENERIC_M4 target

Completes 2e1da01 and fixes arduino/ArduinoCore-mbed#867

Author: facchinm

targets/TARGET_STM/TARGET_STM32H7/TARGET_STM32H747xI/TARGET_GENERIC_STM32H747_M4/PinNames.h

@@ -43,7 +43,7 @@
 extern "C" {
 #endif
 
-#define DUAL_PAD 0xF00
+#define DUAL_PAD 0x800
 
 typedef enum {
     ALT0  = 0x100,

targets/TARGET_STM/tools/STM32_gen_PeripheralPins.py

@@ -491,7 +491,7 @@ def print_header():
 
     if DUAL_PAD:
         line_to_write = ("""
-#define DUAL_PAD 0xF00
+#define DUAL_PAD 0x800
 """)
         out_h_file.write(line_to_write)