phy: Return NULL if the phy is optional

If we're trying to get a handle to an optional phy, then the phy framework
being disabled shouldn't return an hard error.

Instead, return NULL just like phy_optional_get does when there's no phy
provided in the DT.

Signed-off-by: Maxime Ripard <[e-mail]>
Signed-off-by: Kishon Vijay Abraham I <[e-mail]>

include/linux/phy/phy.h

···
 static inline struct phy *devm_phy_optional_get(struct device *dev,
 						const char *string)
 {
-	return ERR_PTR(-ENOSYS);
+	return NULL;
 }
 
 static inline struct phy *devm_of_phy_get(struct device *dev,