fit size should be rounded up instead of rounding down first and adding
a block. Otherwise the calculated size is one block more than needed
when fit size is exactly multiples of one block size.
Fixes: 9a863f803e ("kernel: mtdsplit: add support for FIT image")
Signed-off-by: Chuanhong Guo <gch981213@gmail.com>
Signed-off-by: Qingfang Deng <qingfang.deng@siflower.com.cn>