Iris send backlight info over i2c

keyboards/iris/matrix.c

@@ -208,6 +208,15 @@ int i2c_transaction(void) {
     err = i2c_master_write(0x00);
     if (err) goto i2c_error;
 
+#ifdef BACKLIGHT_ENABLE
+    // Write backlight level for slave to read
+    err = i2c_master_write(get_backlight_level());
+#else
+    // Write zero, so our byte index is the same
+    err = i2c_master_write(0x00);
+#endif
+    if (err) goto i2c_error;
+
     // Start read
     err = i2c_master_start(SLAVE_I2C_ADDRESS + I2C_READ);
     if (err) goto i2c_error;
@@ -285,8 +294,12 @@ void matrix_slave_scan(void) {
     int offset = (isLeftHand) ? 0 : ROWS_PER_HAND;
 
 #ifdef USE_I2C
+#ifdef BACKLIGHT_ENABLE
+    // Read backlight level sent from master and update level on slave
+    backlight_set(i2c_slave_buffer[0]);
+#endif
     for (int i = 0; i < ROWS_PER_HAND; ++i) {
-        i2c_slave_buffer[i] = matrix[offset+i];
+        i2c_slave_buffer[i+1] = matrix[offset+i];
     }
 #else // USE_SERIAL
     for (int i = 0; i < ROWS_PER_HAND; ++i) {