virQEMUCapsReset: also clear out hostCPUModel

After succesfully reading an outdated caps cache from disk,
calling virQEMUCapsReset did not properly clear out the calculated
host CPU model. This lead to a memory leak when the host CPU model
pointer was overwritten later in virQEMUCapsNewForBinaryInternal.

Introduced by commit 68c70118.

src/qemu/qemu_capabilities.c

@@ -3430,6 +3430,9 @@ virQEMUCapsReset(virQEMUCapsPtr qemuCaps)
 
     VIR_FREE(qemuCaps->gicCapabilities);
     qemuCaps->ngicCapabilities = 0;
+
+    virCPUDefFree(qemuCaps->hostCPUModel);
+    qemuCaps->hostCPUModel = NULL;
 }