MdeModulePkg/CapsuleApp: Fix memory leak issue.

MdeModulePkg/CapsuleApp: Fix memory leak issue.

This issue is caused by FileInfoBuffer variable. This is a pointer array
and each elements also pointer to a memory buffer that is allocated and
returned by AllocateCopyPool function.

Cc: Jian J Wang <jian.j.wang@intel.com>
Cc: Hao Wu <hao.a.wu@intel.com>
Cc: Zhang Chao B <chao.b.zhang@intel.com>
Cc: Liming Gao <liming.gao@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Chen A Chen <chen.a.chen@intel.com>
Reviewed-by: Hao Wu <hao.a.wu@intel.com>