Suppress clang-format on one case

Newer version of clang-format will format this pair of braces differently
than clang-format-8, which is the version used in upstream CI. Turn off
clang-format to avoid a clang version update in CI breaking us.
Difference shown below.

```

Change-Id: I1633522f0c028af3cfd395bb143a5ea00410648e
--- a/mainloop.cpp (clang 8.0)
+++ b/mainloop.cpp (clang 10.0)
@@ -80,8 +80,7 @@ void updateSensorInterfaces(InterfaceMap& ifaces, int64_t value)
     {
         switch (iface.first)
         {
-            case InterfaceType::VALUE:
-            {
+            case InterfaceType::VALUE: {
```

Signed-off-by: Kun Yi <kunyi731@gmail.com>
Change-Id: I1339a10173a4632decbe1be6c4d7ab8a397a9f38
diff --git a/mainloop.cpp b/mainloop.cpp
index 4abfc02..bd334a0 100644
--- a/mainloop.cpp
+++ b/mainloop.cpp
@@ -80,6 +80,7 @@
     {
         switch (iface.first)
         {
+            // clang-format off
             case InterfaceType::VALUE:
             {
                 auto& valueIface =
@@ -87,6 +88,7 @@
                 valueIface->value(value);
             }
             break;
+            // clang-format on
             case InterfaceType::WARN:
                 checkThresholds<WarningObject>(iface.second, value);
                 break;