ar71xx: disable flow control to the built-in switch on AR934x

It apparently causes a regression on some devices if the ethernet cable
is plugged in while booting.

Signed-off-by: Felix Fietkau <[email protected]>

target/linux/ar71xx/files/arch/mips/ath79/dev-eth.c

@@ -981,7 +981,6 @@ void __init ath79_register_eth(unsigned int id)
 			pdata->set_speed = ath79_set_speed_dummy;
 
 			pdata->switch_data = &ath79_switch_data;
-			pdata->use_flow_control = 1;
 
 			/* reset the built-in switch */
 			ath79_device_reset_set(AR934X_RESET_ETH_SWITCH);