util: fix cache invalidation of swtpm capabilities

The check for whether the swtpm binary was modified is checking pointers
to the mtime field in two distinct structs, so will always compare
different. This resulted in re-probing swtpm capabilities every time,
as many as 20 times for a single VM launch.

Fixes:

  commit 01cf7a1bb9
  Author: Stefan Berger <stefanb@us.ibm.com>
  Date:   Thu Jul 25 14:22:04 2019 -0400

    tpm: Check whether previously found executables were updated

Reviewed-by: Michal Privoznik <mprivozn@redhat.com>
Reviewed-by: Martin Kletzander <mkletzan@redhat.com>
Reviewed-by: Ján Tomko <jtomko@redhat.com>
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>

src/util/virtpm.c

@@ -301,7 +301,7 @@ virTPMEmulatorInit(void)
                 findit = true;
 
             if (!findit &&
-                &statbuf.st_mtime != &prgs[i].stat->st_mtime)
+                statbuf.st_mtime != prgs[i].stat->st_mtime)
                 findit = true;
         }