phy-rockchip-pcie: remove deassert of phy_rst from exit callback

The deassert of phy_rst from exit callback is incorrect as when
doing phy_exit, we expect the phy_rst is on asserted state which was
done by power_off callback, but not deasserted state. Meanwhile when
disabling clk_pciephy_ref, the assert/deassert signal can't actually
take effect on the phy. So let's fix it anyway.

Signed-off-by: Shawn Lin <shawn.lin@rock-chips.com>
Reviewed-by: Heiko Stuebner <heiko@sntech.de>
Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>