physical: Fix readability-redundant-control-flow

```
/home/andrew/src/openbmc/phosphor-led-sysfs/build/../physical.cpp:57:5: error: redundant return statement at the end of a function with a void return type [readability-redundant-control-flow,-warnings-as-errors]
    return;
    ^~~~~~~
/home/andrew/src/openbmc/phosphor-led-sysfs/build/../physical.cpp:100:5: error: redundant return statement at the end of a function with a void return type [readability-redundant-control-flow,-warnings-as-errors]
    return;
~~~~^~~~~~~
/home/andrew/src/openbmc/phosphor-led-sysfs/build/../physical.cpp:123:5: error: redundant return statement at the end of a function with a void return type [readability-redundant-control-flow,-warnings-as-errors]
    return;
~~~~^~~~~~~
```

Change-Id: I58bf70aa3d565a0449e4c0a85b271512a0cf9742
Signed-off-by: Andrew Jeffery <andrew@aj.id.au>
diff --git a/physical.cpp b/physical.cpp
index f488a41..214e31b 100644
--- a/physical.cpp
+++ b/physical.cpp
@@ -54,7 +54,6 @@
                 Action::Off);
         }
     }
-    return;
 }
 
 auto Physical::state() const -> Action
@@ -97,7 +96,6 @@
 
     led.setTrigger("none");
     led.setBrightness(value);
-    return;
 }
 
 void Physical::blinkOperation()
@@ -119,8 +117,6 @@
     auto factor = this->period() / 100.0;
     led.setDelayOn(dutyOn * factor);
     led.setDelayOff((100 - dutyOn) * factor);
-
-    return;
 }
 
 /** @brief set led color property in DBus*/