phy: core: Fixup return value of phy_exit when !pm_runtime_enabled

When phy_pm_runtime_get_sync() returns -ENOTSUPP, phy_exit() also returns
-ENOTSUPP if !phy->ops->exit. Fix it.
Also move the code to override ret close to the code we got ret.
I think it is less error prone this way.

Signed-off-by: Axel Lin <axel.lin@ingics.com>
Acked-by: Roger Quadros <rogerq@ti.com>
Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>