MdeModulePkg/Setup: Fix incorrect size used in AllocateCopyPool

MdeModulePkg/Setup: Fix incorrect size used in AllocateCopyPool

REF:https://bugzilla.tianocore.org/show_bug.cgi?id=1115

When the type of HiiValue is EFI_IFR_TYPE_BUFFER,
its question type is EFI_IFR_ORDERED_LIST_OP.
And the buffer size allocated for Statement->BufferValue
of orderedList is "Statement->StorageWidth"
in IfrParse.c.

So here when backup the buffer value and copy the size of
"Statement->StorageWidth + sizeof(CHAR16)" is incorrect.

This patch is to fix this issue.

Cc: Eric Dong <eric.dong@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Dandan Bi <dandan.bi@intel.com>
Reviewed-by: Eric Dong <eric.dong@intel.com>