Correction for wrong battery display on tlora_v2_1_16 board (#1120)

* Update variant.h

variants/tlora_v2_1_16/variant.h

@@ -4,6 +4,8 @@
 #define GPS_TX_PIN 13
 
 #define BATTERY_PIN 35 // A battery voltage measurement pin, voltage divider connected here to measure battery voltage
+// ratio of voltage divider = 2.0 (R42=100k, R43=100k)
+#define ADC_MULTIPLIER 2.2 // 2.0 + 10% for correction of display undervoltage.
 
 #define I2C_SDA 21 // I2C pins for this board
 #define I2C_SCL 22
@@ -20,4 +22,4 @@
 #define LORA_DIO0 26 // a No connect on the SX1262 module
 #define LORA_RESET 14
 #define LORA_DIO1 35 // Not really used
-#define LORA_DIO2 34 // Not really used
+#define LORA_DIO2 34 // Not really used