mtd: fix resetbc on nand w/ min I/O size > 2048

mtd: fix resetbc on nand w/ min I/O size > 2048

Fix a bug in linksys_bootcount.c that resetbc  won't work on nand
with min I/O size> 2048.

Check the boot-log entry's intergrity with checksum.

Signed-off-by: Qiyuan Zhang <zhang.github@outlook.com>
Link: https://github.com/openwrt/openwrt/pull/16070
(cherry picked from commit 62da99e6d506f3517f50c1efd61e1911df507ae3)
Signed-off-by: Rafal Boni <rafal.boni@gmail.com>
Link: https://github.com/openwrt/openwrt/pull/17889
Signed-off-by: Robert Marko <robimarko@gmail.com>