MdeModulePkg/PartitionDxe: Add check for underlying device block size

MdeModulePkg/PartitionDxe: Add check for underlying device block size

REF:https://bugzilla.tianocore.org/show_bug.cgi?id=828

Within FindAnchorVolumeDescriptorPointer():

Add a check for the underlying device block size to ensure it is greater
than the size of an Anchor Volume Descriptor Pointer.

Cc: Ruiyu Ni <ruiyu.ni@intel.com>
Cc: Jiewen Yao <jiewen.yao@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Hao Wu <hao.a.wu@intel.com>
Reviewed-by: Paulo Alcantara <palcantara@suse.de>
Acked-by: Star Zeng <star.zeng@intel.com>