kernel: yaffs: use new_sync_{read,write} for 3.18+

kernel: yaffs: use new_sync_{read,write} for 3.18+

Using the do_sync_{read,write} functions in conjunction
with the generic_file_{read,write}_iter causes a kernel
panic like this:

  root@OpenWrt:/# mount -t yaffs /dev/mtdblock5 /mnt
  [ 2884.110000] yaffs: dev is 32505861 name is "mtdblock5" rw
  [ 2884.120000] yaffs: passed flags ""
  root@OpenWrt:/# hexdump -vC -n 64 /mnt/kernel
  [ 2902.700000] CPU 0 Unable to handle kernel paging request at virtual \
    address 00000000, epc == 00000000, ra == 80129414
  [ 2902.710000] Oops[#1]:
  [ 2902.710000] CPU: 0 PID: 1030 Comm: hexdump Not tainted 3.18.9 #2
  [ 2902.710000] task: 878e7a20 ti: 868c6000 task.ti: 868c6000
  [ 2902.710000] $ 0   : 00000000 fffffff8 00000000 00000000
  [ 2902.710000] $ 4   : 868c7e70 868c7ea8 00000001 868c7f08
  [ 2902.710000] $ 8   : 00000038 80064f18 80072280 00000000
  [ 2902.710000] $12   : 7fa152b8 7709e3a0 00c42008 7709e3a0
  [ 2902.710000] $16   : 868c7f08 86a46000 00000010 878e7a20
  [ 2902.710000] $20   : 7705c4b0 00000010 00000000 00000000
  [ 2902.710000] $24   : 770960bc 7707dd78
  [ 2902.710000] $28   : 868c6000 868c7e58 7f8e7030 80129414
  [ 2902.710000] Hi    : 00000000
  [ 2902.710000] Lo    : ffffffff
  [ 2902.710000] epc   : 00000000   (null)
  [ 2902.710000]     Not tainted
  [ 2902.710000] ra    : 80129414 do_sync_read+0x7c/0xb4
  [ 2902.710000] Status: 1900dc03 KERNEL EXL IE
  [ 2902.710000] Cause : 00800008
  [ 2902.710000] BadVA : 00000000
  [ 2902.710000] PrId  : 00019750 (MIPS 74Kc)

Change the yaffs code to use the new_sync_{read,write} functions
instead.

Signed-off-by: Gabor Juhos <juhosg@openwrt.org>
git-svn-id: svn://svn.openwrt.org/openwrt/trunk@44974 3c298f89-4303-0410-b956-a3cf2f4a3e73