ar71xx: fix mtd corruption

ar71xx: fix mtd corruption

In commit 9e1530b2a35e ("kernel: bump 4.9 to 4.9.117 for 18.06") [1], the following patch for removed:
- 403-mtd_fix_cfi_cmdset_0002_status_check.patch

This patch contained fixes for both write and erase functions.

While the chip-detects for erase got fixed upstream [2],
some modifications are still required, even with the fixes applied.

Not doing so results in following errors seen:

Collected errors:
 * pkg_write_filelist: Failed to open //usr/lib/opkg/info/luci-lib-ip.list: I/O error.
 * opkg_install_pkg: Failed to extract data files for luci-lib-ip. Package debris may remain!
 * opkg_install_cmd: Cannot install package luci-ssl.
 * opkg_conf_write_status_files: Can't open status file //usr/lib/opkg/status: I/O error.

[    0.780920] jffs2: version 2.2 (NAND) (SUMMARY) (LZMA) (RTIME) (CMODE_PRIORITY) (c) 2001-2006 Red Hat, Inc.
[    8.406396] jffs2: notice: (415) jffs2_build_xattr_subsystem: complete building xattr subsystem, 0 of xdatum (0 unchecked, 0 orphan) and 0 of xref (0 dead, 0 orphan) found.
[    8.423476] mount_root: switching to jffs2 overlay
[  270.902671] jffs2: Write of 1989 bytes at 0x005ce6f8 failed. returned -5, retlen 962
[  270.931965] jffs2: Write of 1989 bytes at 0x005ceec0 failed. returned -5, retlen 0
[  270.939631] jffs2: Not marking the space at 0x005ceec0 as dirty because the flash driver returned retlen zero
[  270.950397] jffs2: Write of 68 bytes at 0x005ceec0 failed. returned -5, retlen 0
[  270.957838] jffs2: Not marking the space at 0x005ceec0 as dirty because the flash driver returned retlen zero
[  270.968584] jffs2: Write of 68 bytes at 0x005ceec0 failed. returned -5, retlen 0
[  270.976027] jffs2: Not marking the space at 0x005ceec0 as dirty because the flash driver returned retlen zero
[  270.986735] jffs2: Write of 68 bytes at 0x005ceec0 failed. returned -5, retlen 0
[  270.994225] jffs2: Not marking the space at 0x005ceec0 as dirty because the flash driver returned retlen zero

[1] https://git.openwrt.org/?p=openwrt/openwrt.git;a=commit;h=fec8fe806963c96a6506c2aebc3572d3a11f285f
[2] https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?h=v4.9.133&id=a0239d83e1cb60de5e78452d4708c083b9e3dcbe

Fixes: 9e1530b2a35e ("kernel: bump 4.9 to 4.9.117 for 18.06")
Signed-off-by: Fabio Bettoni <fbettoni@gmail.com>
Signed-off-by: Koen Vandeputte <koen.vandeputte@ncentric.com>