item_updater: Ignore base version when trying to free up priority.

- There is a bug in our code where a user can try to allocate the
  existing priority of a version to itself and this would cause
  all subsequent priorities to be incremented by 2 instead of 1.
- By checking the base versionId we can skip the operation to free
  the priority of the base version since it will be reassigned.

Resolves openbmc/openbmc#2075

Change-Id: Ice21d701bb2e964c5734273f4e8a3821b96f4830
Signed-off-by: Saqib Khan <khansa@us.ibm.com>
diff --git a/item_updater.hpp b/item_updater.hpp
index 934ec3c..2f3b1ea 100755
--- a/item_updater.hpp
+++ b/item_updater.hpp
@@ -46,10 +46,11 @@
          *  any existing priority with the same value by 1
          *
          *  @param[in] value - The priority that needs to be set free.
-         *
+         *  @param[in] versionId - The Id of the version for which we
+         *                         are trying to free up the priority.
          *  @return None
          */
-        void freePriority(uint8_t value);
+        void freePriority(uint8_t value, const std::string& versionId);
 
         /** @brief Determine is the given priority is the lowest
          *