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/fru_identity.cpp b/extensions/openpower-pels/fru_identity.cpp
index d6a2968..4b765fd 100644
--- a/extensions/openpower-pels/fru_identity.cpp
+++ b/extensions/openpower-pels/fru_identity.cpp
@@ -51,7 +51,7 @@
     }
 }
 
-}; // namespace
+} // namespace
 
 FRUIdentity::FRUIdentity(Stream& pel)
 {