net: ethernet: ti: cpsw: fix extra rx interrupt

Now RX interrupt is triggered twice every time, because in
cpsw_rx_interrupt() it is asked first and then disabled. So there will be
pending interrupt always, when RX interrupt is enabled again in NAPI
handler.

Fix it by first disabling IRQ and then do ask.

Fixes: 870915fe

 ("drivers: net: cpsw: remove disable_irq/enable_irq as irq can be masked from cpsw itself")
Signed-off-by: Grygorii Strashko <grygorii.strashko@ti.com>
Signed-off-by: David S. Miller <davem@davemloft.net>