ShellPkg/memmap: Refine code

The patch changes Buffer to Descriptors, changes
(UINT8 *Walker) to (EFI_MEMORY_DESCRIPTOR *Walker).
The change makes lots of type conversion unnecessary.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Ruiyu Ni <ruiyu.ni@intel.com>
Reviewed-by: Jaben Carsey <jaben.carsey@intel.com>
(cherry picked from commit ac25ebdccc667ecf8397c7310f66e8e2fcfacb26)
1 file changed