physical: Fix cppcoreguidelines-pro-type-member-init

```
/home/andrew/src/openbmc/phosphor-led-sysfs/build/../physical.hpp:48:5: error: constructor does not initialize these fields: assert [cppcoreguidelines-pro-type-member-init,-warnings-as-errors]
    Physical(sdbusplus::bus_t& bus, const std::string& objPath, SysfsLed& led,
    ^
```

Change-Id: I1e05ee113132fa39d0590897a1e3e0977c6ceecb
Signed-off-by: Andrew Jeffery <andrew@aj.id.au>
diff --git a/physical.hpp b/physical.hpp
index 885bf55..b057362 100644
--- a/physical.hpp
+++ b/physical.hpp
@@ -81,7 +81,7 @@
     SysfsLed& led;
 
     /** @brief The value that will assert the LED */
-    unsigned long assert;
+    unsigned long assert{};
 
     /** @brief reads sysfs and then setsup the parameteres accordingly
      *