leds: trigger: netdev: uninitialized variable in netdev_trig_activate()

The qca8k_cled_hw_control_get() function which implements ->hw_control_get
sets the appropriate bits but does not clear them.  This leads to an
uninitialized variable bug.  Fix this by setting mode to zero at the
start.

Fixes: e0256648 ("net: dsa: qca8k: implement hw_control ops")
Signed-off-by: Dan Carpenter <dan.carpenter@linaro.org>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Acked-by: Lee Jones <lee@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>