Fix a misuse of virAsprintf in qemudDomainMemoryPeek

The code specifies driver->cacheDir as the format string,
but it usually doesn't contain '%s', so the subsequent
argument, "/qemu.mem.XXXXXX", is always ignored.

The patch fixes the misuse.

src/qemu/qemu_driver.c

@@ -9177,7 +9177,7 @@ qemudDomainMemoryPeek (virDomainPtr dom,
         goto endjob;
     }
 
-    if (virAsprintf(&tmp, driver->cacheDir,  "/qemu.mem.XXXXXX") < 0) {
+    if (virAsprintf(&tmp, "%s/qemu.mem.XXXXXX", driver->cacheDir) < 0) {
         virReportOOMError();
         goto endjob;
     }