fixed PowerState enum cast

Quite a while ago I made a commit (131631b) where I did a weird
thing to fix compilation with PTRCALL_ENABLED. And I couldn't
sleep because of this after all these months. So here is the
proper version.

core/method_ptrcall.h

@@ -115,7 +115,6 @@ MAKE_PTRARG(PoolVector2Array);
 MAKE_PTRARG(PoolVector3Array);
 MAKE_PTRARG(PoolColorArray);
 MAKE_PTRARG(Variant);
-MAKE_PTRARG(PowerState);
 
 //this is for Object
 

core/os/os.h

@@ -413,4 +413,6 @@ public:
 	virtual ~OS();
 };
 
+VARIANT_ENUM_CAST(PowerState);
+
 #endif