build: fix typo in debug message

Introduced in commit 0caccb58.

  CC     libvirt_driver_qemu_impl_la-qemu_capabilities.lo
../../src/qemu/qemu_capabilities.c: In function 'qemuCapsInitQMP':
../../src/qemu/qemu_capabilities.c:2327:13: error: format '%d' expects argument of type 'int', but argument 8 has type 'const char *' [-Werror=format]

* src/qemu/qemu_capabilities.c (qemuCapsInitQMP): Use correct format.

src/qemu/qemu_capabilities.c

@@ -2324,7 +2324,7 @@ cleanup:
         int rc;
 
         if ((rc = virPidFileReadPath(pidfile, &pid)) < 0) {
-            VIR_DEBUG("Failed to read pidfile %s: %d",
+            VIR_DEBUG("Failed to read pidfile %s: %s",
                       pidfile, virStrerror(-rc, ebuf, sizeof(ebuf)));
         } else {
             VIR_DEBUG("Killing QMP caps process %lld", (long long) pid);