MdeModulePkg CapsuleApp: Fix print info in BuildGatherList()

REF: https://bugzilla.tianocore.org/show_bug.cgi?id=614



Print (L"CapsuleApp: capsule data starts          at 0x%X with
 size 0x%X\n", (UINTN) CapsuleBuffer, FileSize);

It should use (UINTN) CapsuleBuffer[Index] and FileSize[Index]
as parameter.

Cc: Jiewen Yao <jiewen.yao@intel.com>
Cc: Cloud Wang <winggundum82@163.com>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Star Zeng <star.zeng@intel.com>
Reviewed-by: Jiewen Yao <jiewen.yao@intel.com>