catch exceptions as const

Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
Change-Id: I0bb9caa5bff2c57ea331b9982f279753c44d69d4
diff --git a/ibm_vpd_utils.cpp b/ibm_vpd_utils.cpp
index b8af0ed..822049c 100644
--- a/ibm_vpd_utils.cpp
+++ b/ibm_vpd_utils.cpp
@@ -239,7 +239,7 @@
             present = true;
         }
     }
-    catch (json::parse_error& ex)
+    catch (const json::parse_error& ex)
     {
         throw(VpdJsonException("Json Parsing failed", INVENTORY_JSON_SYM_LINK));
     }
@@ -277,7 +277,7 @@
                 }
             }
         }
-        catch (json::parse_error& ex)
+        catch (const json::parse_error& ex)
         {
             throw(VpdJsonException("Json Parsing failed", DBUS_PROP_JSON));
         }
@@ -416,7 +416,7 @@
         jsonPath += jsonName;
     }
 
-    catch (json::parse_error& ex)
+    catch (const json::parse_error& ex)
     {
         throw(VpdJsonException("Json Parsing failed", SYSTEM_JSON));
     }