boards/limifrog-v1: adapted I2C config

boards/limifrog-v1/include/periph_conf.h

@@ -150,9 +150,9 @@ static const timer_conf_t timer_config[] = {
 static const i2c_conf_t i2c_config[] = {
     /* device, port, scl-, sda-pin-number, I2C-AF, ER-IRQn, EV-IRQn */
     {I2C1, GPIO_PIN(PORT_B,  8), GPIO_PIN(PORT_B,  9),
-     GPIO_AF4, I2C1_ER_IRQn, I2C1_EV_IRQn},
+     GPIO_OD_PU, GPIO_AF4, I2C1_ER_IRQn, I2C1_EV_IRQn},
     {I2C2, GPIO_PIN(PORT_B, 10), GPIO_PIN(PORT_B, 11),
-     GPIO_AF4, I2C2_ER_IRQn, I2C2_EV_IRQn},
+     GPIO_OD_PU, GPIO_AF4, I2C2_ER_IRQn, I2C2_EV_IRQn},
 };
 
 /** @} */