[openwrt/openwrt] mtd: fix erase handling with partition offset on write

[LEDE Commits]

nbd pushed a commit to openwrt/openwrt.git, branch master:
https://git.lede-project.org/d92ec071b211e0ee17496287f62652beb7db543d

commit d92ec071b211e0ee17496287f62652beb7db543d
Author: Felix Fietkau <nbd at nbd.name>
AuthorDate: Fri Apr 20 10:02:28 2018 +0200

    mtd: fix erase handling with partition offset on write
    
    When a partition offset is given, it is used in an lseek call, which
    affects write, but not erase. Add it to the offset for erase calls as
    well
    
    Signed-off-by: Felix Fietkau <nbd at nbd.name>
---
 package/system/mtd/src/mtd.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/package/system/mtd/src/mtd.c b/package/system/mtd/src/mtd.c
index 55a3bdb..fa04c0f 100644
--- a/package/system/mtd/src/mtd.c
+++ b/package/system/mtd/src/mtd.c
@@ -638,7 +638,7 @@ resume:
 					continue;
 				}
 
-				if (mtd_erase_block(fd, e) < 0) {
+				if (mtd_erase_block(fd, e + part_offset) < 0) {
 					if (next) {
 						if (w < e) {
 							write(fd, buf + offset, e - w);