net: mvpp2: fix polarity of PHY reset signal

The dm_gpio_set_value() call sets the logical level of the GPIO signal.
That is, it takes the GPIO_ACTIVE_{LOW,HIGH} property into account. The
driver needs to assert the reset, and then deassert it. Not the other
way around.

Cc: Stefan Chulski <stefanc@marvell.com>
Signed-off-by: Baruch Siach <baruch@tkos.co.il>
Acked-by: Joe Hershberger <joe.hershberger@ni.com>
Reviewed-by: Stefan Roese <sr@denx.de>