openpower-pels: clean up various compile warnings

Compile warnings observed when compiling parts of the
openpower-pels (or corresponding tests) under stricter
compiler warning flags of Meson.

Issues fixed:
    - many unused parameters
    - invalid case fall-through
    - excess semi-colons
    - incorrect 'const' on return-by-value type
    - removal of variable length array in test case
    - uncaught return from 'system' call in test case

Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
Change-Id: I8af69184042cf8661d1307a02ecf3afcab4724a1
diff --git a/extensions/openpower-pels/host_notifier.cpp b/extensions/openpower-pels/host_notifier.cpp
index 8760a8b..496f1c3 100644
--- a/extensions/openpower-pels/host_notifier.cpp
+++ b/extensions/openpower-pels/host_notifier.cpp
@@ -228,7 +228,7 @@
                                           this, std::placeholders::_1));
 }
 
-void HostNotifier::dispatch(sdeventplus::source::EventBase& source)
+void HostNotifier::dispatch(sdeventplus::source::EventBase& /*source*/)
 {
     _dispatcher.reset();