ptable: correct the last usable block number
ptable: correct the last usable block number

Correct the last usable block number of emmc on hikey.

Signed-off-by: Haojian Zhuang <979139d45d262f0480136b0da512e0afa0fe79d3@gmail.com>

96boards-hikey/l-loader,96boards-hikey/l-loader