fix warnings

Fix a couple warnings so we can use meson warning level 3.  Instances of
the following warnings are found and resolved:

  Wreorder
  Wsign-compare

Change-Id: Ia223b42aa6bf743cfa0e7042cc3d5a18977459be
Signed-off-by: Brad Bishop <bradleyb@fuzziesquirrel.com>
diff --git a/src/PSUSensorMain.cpp b/src/PSUSensorMain.cpp
index eed0168..3d386e4 100644
--- a/src/PSUSensorMain.cpp
+++ b/src/PSUSensorMain.cpp
@@ -544,7 +544,7 @@
             {
                 /* Find out sensor name index for this label */
                 std::regex rgx("[A-Za-z]+([0-9]+)");
-                int nameIndex{0};
+                size_t nameIndex{0};
                 if (std::regex_search(labelHead, matches, rgx))
                 {
                     nameIndex = std::stoi(matches[1]);