phosphor-ipmi-flash: Code Health Cleanup

Removed the following warning.
- using decl '*' is unused
- 'push_back' is called inside a loop; consider pre-allocating the
    container capacity before the loop
- function '*' defined in a header file; function
    definitions in header files can lead to ODR violations

Change-Id: I44e4b0f8056a853fb45b690394be1a8ebec45b20
Signed-off-by: Willy Tu <wltu@google.com>
diff --git a/bmc/firmware-handler/firmware_handler.cpp b/bmc/firmware-handler/firmware_handler.cpp
index afcfc81..9268809 100644
--- a/bmc/firmware-handler/firmware_handler.cpp
+++ b/bmc/firmware-handler/firmware_handler.cpp
@@ -56,10 +56,10 @@
     }
 
     std::vector<std::string> blobs;
-    for (const auto& item : firmwares)
-    {
-        blobs.push_back(item.blobName);
-    }
+    blobs.reserve(firmwares.size());
+    std::for_each(
+        firmwares.begin(), firmwares.end(),
+        [&blobs](const auto& blob) { blobs.emplace_back(blob.blobName); });
 
     if (0 == std::count(blobs.begin(), blobs.end(), hashBlobId))
     {