vircgroupv2: fix setting cpu.max period

When we set cpu.max period we need to parse the cpu.max file first as
it contains both quota and period values separated by space.  When only
a single number is written to that file it will set quota.  However,
in order to change period we need to write both values.

The code was prepared for that but mistakenly used new line to end the
string with the first value.

Resolves: https://bugzilla.redhat.com/show_bug.cgi?id=1749227

Signed-off-by: Pavel Hrdina <phrdina@redhat.com>
Reviewed-by: Erik Skultety <eskultet@redhat.com>

src/util/vircgroupv2.c

@@ -1508,7 +1508,7 @@ virCgroupV2SetCpuCfsPeriod(virCgroupPtr group,
                        _("Invalid 'cpu.max' data."));
         return -1;
     }
-    *tmp = '\n';
+    *tmp = '\0';
 
     if (virAsprintf(&value, "%s %llu", str, cfs_period) < 0)
         return -1;