make explicit we return chars

server/drivers/hd44780-bwct-usb.c

@@ -198,7 +198,7 @@ bwct_usb_HD44780_backlight(PrivateData *p, unsigned char state)
 unsigned char
 bwct_usb_HD44780_scankeypad(PrivateData *p)
 {
-  return 0;
+  return '\0';
 }
 
 

server/drivers/hd44780-lcd2usb.c

@@ -159,7 +159,7 @@ lcd2usb_HD44780_scankeypad(PrivateData *p)
     return buffer[0];
   }
 
-  return 0;
+  return '\0';
 }
 
 void

server/drivers/hd44780-lis2.c

@@ -214,7 +214,7 @@ void lis2_HD44780_backlight(PrivateData *p, unsigned char state)
 
 unsigned char lis2_HD44780_scankeypad(PrivateData *p)
 {
-	return 0;
+	return '\0';
 }