catch exceptions as const

Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
Change-Id: If6aba71f482f75143e6d669763b8853db22318cf
diff --git a/phosphor-power-supply/psu_manager.cpp b/phosphor-power-supply/psu_manager.cpp
index 603c0ef..ee21a81 100644
--- a/phosphor-power-supply/psu_manager.cpp
+++ b/phosphor-power-supply/psu_manager.cpp
@@ -125,7 +125,7 @@
                     std::get_if<std::string>(&properties[presLineName]);
             }
         }
-        catch (std::exception& e)
+        catch (const std::exception& e)
         {}
     }
 
@@ -221,7 +221,7 @@
 
         supportedConfigs.emplace(*model, sys);
     }
-    catch (std::exception& e)
+    catch (const std::exception& e)
     {}
 }
 
@@ -249,7 +249,7 @@
             populateSysProperties(properties);
         }
     }
-    catch (std::exception& e)
+    catch (const std::exception& e)
     {
         // Interface or property not found. Let the Interfaces Added callback
         // process the information once the interfaces are added to D-Bus.
@@ -288,7 +288,7 @@
             validateConfig();
         }
     }
-    catch (std::exception& e)
+    catch (const std::exception& e)
     {
         // Ignore, the property may be of a different type than expected.
     }
@@ -350,7 +350,7 @@
 
         auto reply = bus.call(method);
     }
-    catch (std::exception& e)
+    catch (const std::exception& e)
     {
         log<level::ERR>(
             fmt::format(