clang-tidy: Enable readability-convert-member-functions-to-static

This check finds non-static member functions that can be made
static because the functions don’t use this.
This check also triggers readability-static-accessed-through
-instance check as we are trying to access a static member
function through an instance.

Change-Id: Ia0867db019db8e40e710bdd4025e030061f7a992
Signed-off-by: Pavithra Barithaya <pavithrabarithaya07@gmail.com>
diff --git a/item_updater.hpp b/item_updater.hpp
index a0607fe..ad538e9 100644
--- a/item_updater.hpp
+++ b/item_updater.hpp
@@ -290,8 +290,8 @@
      *                      true if all image files are found in BMC tarball
      *                      false if one of image files is missing
      */
-    bool checkImage(const std::string& filePath,
-                    const std::vector<std::string>& imageList);
+    static bool checkImage(const std::string& filePath,
+                           const std::vector<std::string>& imageList);
 
     /** @brief Persistent MinimumVersion D-Bus object */
     std::unique_ptr<MinimumVersion> minimumVersionObject;