ar71xx/ath79: fix mtd corruption

ar71xx/ath79: fix mtd corruption

In commit fec8fe806963 ("kernel: bump 4.9 to 4.9.116") [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.

While at it, also apply the same fix for target ath79,
which suffers the same issue.

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: fec8fe806963 ("kernel: bump 4.9 to 4.9.116")
Signed-off-by: Fabio Bettoni <fbettoni@gmail.com>
Signed-off-by: Koen Vandeputte <koen.vandeputte@ncentric.com>