ShellPkg/UefiShellBcfgCommandLib: Fix VS2012 build failure

Cc: Ruiyu Ni <ruiyu.ni@intel.com>
Cc: Jaben Carsey <jaben.carsey@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Dandan Bi <dandan.bi@intel.com>
Reviewed-by: Jaben Carsey <jaben.carsey@intel.com>
Reviewed-by: Ruiyu Ni <ruiyu.ni@intel.com>

ShellPkg/Library/UefiShellBcfgCommandLib/UefiShellBcfgCommandLib.c

@@ -402,6 +402,7 @@ BcfgMod (
   ShellStatus       = SHELL_SUCCESS;
   FileList          = NULL;
   DevicePath        = NULL;
+  DevicePathBuffer  = NULL;
 
   ZeroMem (&LoadOption, sizeof(EFI_BOOT_MANAGER_LOAD_OPTION));