[][OpenWrt Dev][nmbm: add extra bad block check before erasing]

[Description]
Add extra bad block check before erasing to make sure bad block(s) marked
by user after NMBM initialization can be detected.

[Release-log]
N/A

Change-Id: I1dcacb37210c710db0ab259c5068a120004b1f28
Reviewed-on: https://gerrit.mediatek.inc/c/openwrt/feeds/mtk_openwrt_feeds/+/4649340
1 file changed