MdeModulePkg DxeCapsuleLibFmp: Refine the code to check FmpImageSize
The code to check FmpImageSize again OFFSET_OF
(EFI_FIRMWARE_MANAGEMENT_CAPSULE_IMAGE_HEADER, UpdateHardwareInstance)
can be refined to check against FmpImageHeaderSize.
Cc: Jiewen Yao <jiewen.yao@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.1 Signed-off-by: Star Zeng <star.zeng@intel.com> Reviewed-by: Jiewen Yao <jiewen.yao@intel.com>