ShellPkg: BcfgDisplayDump(): address FilePathListLength by name

ShellPkg: BcfgDisplayDump(): address FilePathListLength by name

The Buffer variable points at the beginning of an EFI_LOAD_OPTION
structure. We might as well address the "FilePathListLength" member by
name, rather than with *(UINT16*)(Buffer+4).

This patch is not supposed to change behavior.

Cc: Jaben Carsey <jaben.carsey@intel.com>
Cc: Ryan Harkin <ryan.harkin@linaro.org>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Jaben Carsey <jaben.carsey@intel.com>
git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@19711 6f19259b-4bc3-4df7-8a09-765794883524