fs: Fix '<' comparison of value produced by logical not '!'

Commit da665fbd introduced the following condition to virLXCProcessEnsureRootFS
and openvzReadFSConf:

if (!(<some_var> = virDomainFSDefNew()) < 0)

which broke the build on fedora with GCC 5.3.1: "logical not is only applied to
the left hand side of comparison".
Signed-off-by: NErik Skultety <eskultet@redhat.com>

src/lxc/lxc_process.c

@@ -1153,7 +1153,7 @@ virLXCProcessEnsureRootFS(virDomainObjPtr vm)
     if (root)
         return 0;
 
-    if (!(root = virDomainFSDefNew()) < 0)
+    if (!(root = virDomainFSDefNew()))
         goto error;
 
     root->type = VIR_DOMAIN_FS_TYPE_MOUNT;

src/openvz/openvz_conf.c

@@ -351,7 +351,7 @@ openvzReadFSConf(virDomainDefPtr def,
                        veid);
         goto error;
     } else if (ret > 0) {
-        if (!(fs = virDomainFSDefNew()) < 0)
+        if (!(fs = virDomainFSDefNew()))
             goto error;
 
         fs->type = VIR_DOMAIN_FS_TYPE_TEMPLATE;