net: stmmac: fix reset gpio free missing

[ Upstream commit 49ce881c0d4c4a7a35358d9dccd5f26d0e56fc61 ]

Commit 984203ce ("net: stmmac: mdio: remove reset gpio free")
removed the reset gpio free, when the driver is unbinded or rmmod,
we miss the gpio free.

This patch uses managed API to request the reset gpio, so that the
gpio could be freed properly.

Fixes: 984203ce ("net: stmmac: mdio: remove reset gpio free")
Signed-off-by: Jisheng Zhang <Jisheng.Zhang@synaptics.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>