mcu/pic32: Fix I2C_4 configuration typo

For I2C_4 (if enabled) configuration was using i2c_3_cfg data
instead of i2c_4_cfg, it is now corrected.

Signed-off-by: Jerzy Kasenberg <jerzy.kasenberg@codecoup.pl>

hw/mcu/microchip/pic32mz/src/pic32mz_periph.c

@@ -471,7 +471,7 @@ pic32mz_periph_i2c_devs(void)
     }
 
     if (MYNEWT_VAL(I2C_4)) {
-        rc = hal_i2c_init(4, (void *)&i2c_3_cfg);
+        rc = hal_i2c_init(4, (void *)&i2c_4_cfg);
         assert(rc == 0);
     }
 }