net: phy: marvell: clear wol event before setting it

If WOL event happened once, the LED[2] interrupt pin will not be
cleared unless we read the CSISR register. If interrupts are in use,
the normal interrupt handling will clear the WOL event. Let's clear the
WOL event before enabling it if !phy_interrupt_is_valid().

Signed-off-by: Jingju Hou <Jingju.Hou@synaptics.com>
Signed-off-by: Jisheng Zhang <Jisheng.Zhang@synaptics.com>
Signed-off-by: David S. Miller <davem@davemloft.net>