EmbeddedPkg: Fix a build error in FwVol.c in X64 arch

EmbeddedPkg: Fix a build error in FwVol.c in X64 arch

BZ: https://bugzilla.tianocore.org/show_bug.cgi?id=3814

CompressedDataLength is declared as UINTN which is UINT64 in X64 arch.
But the second parameter of UefiDecompressGetInfo() is declared as
UINT32. So a build error is triggered. To declare CompressedDataLength
as UINT32 to fix the build error.

Cc: Leif Lindholm <leif@nuviainc.com>
Cc: Ard Biesheuvel <ardb+tianocore@kernel.org>
Cc: Abner Chang <abner.chang@hpe.com>
Cc: Daniel Schaefer <daniel.schaefer@hpe.com>
Signed-off-by: Min Xu <min.m.xu@intel.com>