qemu: domain: Add macro to simplify access to vm private data

Sometimes adding a separate variable to access vm->privateData is not
necessary. Add a macro that will do the typecasting rather than having
to add a temp variable to force the compiler to typecast it.

src/qemu/qemu_domain.h

@@ -234,6 +234,9 @@ struct _qemuDomainObjPrivate {
     size_t masterKeyLen;
 };
 
+# define QEMU_DOMAIN_PRIVATE(vm)	\
+    ((qemuDomainObjPrivatePtr) (vm)->privateData)
+
 /* Type of domain secret */
 typedef enum {
     VIR_DOMAIN_SECRET_INFO_TYPE_PLAIN = 0,