qemu: domain: Fix logic bug in qemuDomainStorageSourceAccessAllow

In commit 76b9aba2 I tried to refactor qemuDomainStorageSourceAccessAllow
but used wrong operators for adding bitwise flags.

This way the flags would result in 0 if any of them would be applied.
Signed-off-by: NPeter Krempa <pkrempa@redhat.com>
Reviewed-by: NJán Tomko <jtomko@redhat.com>

src/qemu/qemu_domain.c

@@ -9491,10 +9491,10 @@ qemuDomainStorageSourceAccessAllow(virQEMUDriverPtr driver,
     qemuDomainStorageSourceAccessFlags flags = QEMU_DOMAIN_STORAGE_SOURCE_ACCESS_SKIP_REVOKE;
 
     if (readonly)
-        flags &= QEMU_DOMAIN_STORAGE_SOURCE_ACCESS_READ_ONLY;
+        flags |= QEMU_DOMAIN_STORAGE_SOURCE_ACCESS_READ_ONLY;
 
     if (!newSource)
-        flags &= QEMU_DOMAIN_STORAGE_SOURCE_ACCESS_MODIFY_ACCESS;
+        flags |= QEMU_DOMAIN_STORAGE_SOURCE_ACCESS_MODIFY_ACCESS;
 
     return qemuDomainStorageSourceAccessModify(driver, vm, elem, flags);
 }