virsh: free the caps list properly if one of them is invalid

VIR_FREE(caps) is not enough to free an array allocated
by vshStringToArray.

==17== 4 bytes in 1 blocks are definitely lost in loss record 4 of 728
==17==    by 0x4EFFC44: virStrdup (virstring.c:554)
==17==    by 0x128B10: _vshStrdup (virsh.c:125)
==17==    by 0x129164: vshStringToArray (virsh.c:218)
==17==    by 0x157BB3: cmdNodeListDevices (virsh-nodedev.c:409)

https://bugzilla.redhat.com/show_bug.cgi?id=1001536

tools/virsh-nodedev.c

@@ -413,8 +413,8 @@ cmdNodeListDevices(vshControl *ctl, const vshCmd *cmd ATTRIBUTE_UNUSED)
     for (i = 0; i < ncaps; i++) {
         if ((cap_type = virNodeDevCapTypeFromString(caps[i])) < 0) {
             vshError(ctl, "%s", _("Invalid capability type"));
-            VIR_FREE(caps);
-            return false;
+            ret = false;
+            goto cleanup;
         }
 
         switch (cap_type) {