Add defaultmotherboard path variable

Added missing variable `defaultmotherboardpath`.
This variable is used under meson flag `custom-dbus-path`
The build failed as this variable was missing.

Tested:
Build passes now

Change-Id: I324879ac43b3d1236be8fe74e641fba4e484dd4a
Signed-off-by: Prithvi Pai <ppai@nvidia.com>
diff --git a/include/smbios_mdrv2.hpp b/include/smbios_mdrv2.hpp
index 848e41f..1bf7733 100644
--- a/include/smbios_mdrv2.hpp
+++ b/include/smbios_mdrv2.hpp
@@ -176,6 +176,9 @@
 
 static constexpr const char* firmwarePath = "/xyz/openbmc_project/software";
 
+static constexpr const char* defaultMotherboardPath =
+    "/xyz/openbmc_project/inventory/system/chassis/motherboard";
+
 constexpr std::array<SMBIOSVersion, 8> supportedSMBIOSVersions{
     SMBIOSVersion{3, 0}, SMBIOSVersion{3, 2}, SMBIOSVersion{3, 3},
     SMBIOSVersion{3, 4}, SMBIOSVersion{3, 5}, SMBIOSVersion{3, 6},