catch exceptions as const

Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
Change-Id: Ic2b49715c7b81ac5bcfc12ff2d3b4c593cd95ce7
diff --git a/dbus-sdr/sdrutils.cpp b/dbus-sdr/sdrutils.cpp
index 7788050..ede14bf 100644
--- a/dbus-sdr/sdrutils.cpp
+++ b/dbus-sdr/sdrutils.cpp
@@ -73,7 +73,7 @@
             auto mapperReply = dbus->call(mapperCall);
             mapperReply.read(sensorTreePartial);
         }
-        catch (sdbusplus::exception_t& e)
+        catch (const sdbusplus::exception_t& e)
         {
             phosphor::logging::log<phosphor::logging::level::ERR>(
                 "fail to update subtree",
@@ -264,7 +264,7 @@
     {
         return sensorNumMapPtr->right.at(path);
     }
-    catch (std::out_of_range& e)
+    catch (const std::out_of_range& e)
     {
         phosphor::logging::log<phosphor::logging::level::ERR>(e.what());
         return invalidSensorNumber;
@@ -298,7 +298,7 @@
     {
         return sensorNumMapPtr->left.at(sensorNum);
     }
-    catch (std::out_of_range& e)
+    catch (const std::out_of_range& e)
     {
         phosphor::logging::log<phosphor::logging::level::ERR>(e.what());
         return std::string();