net: dsa: microchip: lan937x: clear the POR_READY_INT status bit

In the lan937x_reset_switch(), it masks all the switch and port
registers. In the Global_Int_status register, POR ready bit is write 1
to clear bit and all other bits are read only. So, this patch clear the
por_ready_int status bit by writing 1.

Signed-off-by: Arun Ramadoss <arun.ramadoss@microchip.com>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>