qemu: Fix the wrong expression

Wrong use of the parentheses causes "rc" always having a boolean value,
either "1" or "0", and thus we can't get the detailed error message
when it fails:

Before (I only have 1 node):
% virsh numatune f18 --nodeset 12
error: Unable to change numa parameters
error: unable to set numa tunable: Unknown error -1

After:
virsh numatune f18 --nodeset 12
error: Unable to change numa parameters
error: unable to set numa tunable: Invalid argument

src/qemu/qemu_driver.c

@@ -7470,7 +7470,7 @@ qemuDomainSetNumaParameters(virDomainPtr dom,
                     continue;
                 }
 
-                if ((rc = virCgroupSetCpusetMems(priv->cgroup, nodeset_str) != 0)) {
+                if ((rc = virCgroupSetCpusetMems(priv->cgroup, nodeset_str)) != 0) {
                     virReportSystemError(-rc, "%s",
                                          _("unable to set numa tunable"));
                     virBitmapFree(nodeset);