psu-ng : add header to SerialNumber property

The VINI SN property has header + SerialNumber but the serial number was
missing the header.

Signed-off-by: Mike Capps <mikepcapps@gmail.com>
Change-Id: I8b1d67ccced5ca3c244e57ca041f2ee11872e111
diff --git a/phosphor-power-supply/power_supply.cpp b/phosphor-power-supply/power_supply.cpp
index 4771183..864ae0e 100644
--- a/phosphor-power-supply/power_supply.cpp
+++ b/phosphor-power-supply/power_supply.cpp
@@ -814,7 +814,7 @@
             header =
                 pmbusIntf->readString(SERIAL_HEADER, Type::HwmonDeviceDebug);
             sn = pmbusIntf->readString(SERIAL_NUMBER, Type::HwmonDeviceDebug);
-            assetProps.emplace(SN_PROP, sn);
+            assetProps.emplace(SN_PROP, header + sn);
         }
         catch (const ReadFailure& e)
         {