f2fs: fix to avoid use SSR allocate when do defragment

SSR allocate mode will be used when doing file defragment
if ATGC is working at the same time, that is because
set_page_private_gcing may make CURSEG_ALL_DATA_ATGC segment
type got in f2fs_allocate_data_block when defragment page
is writeback, which may cause file fragmentation is worse.

A file with 2 fragmentations is changed as following after defragment:

----------------file info-------------------
sensorsdata :
--------------------------------------------
dev       [254:48]
ino       [0x    3029 : 12329]
mode      [0x    81b0 : 33200]
nlink     [0x       1 : 1]
uid       [0x    27e6 : 10214]
gid       [0x    27e6 : 10214]
size      [0x  242000 : 2367488]
blksize   [0x    1000 : 4096]
blocks    [0x    1210 : 4624]
--------------------------------------------

file_pos   start_blk     end_blk        blks
       0    11361121    11361207          87
  356352    11361215    11361216           2
  364544    11361218    11361218           1
  368640    11361220    11361221           2
  376832    11361224    11361225           2
  385024    11361227    11361238          12
  434176    11361240    11361252          13
  487424    11361254    11361254           1
  491520    11361271    11361279           9
  528384     3681794     3681795           2
  536576     3681797     3681797           1
  540672     3681799     3681799           1
  544768     3681803     3681803           1
  548864     3681805     3681805           1
  552960     3681807     3681807           1
  557056     3681809     3681809           1

Signed-off-by: Zhiguo Niu <zhiguo.niu@unisoc.com>
Reviewed-by: Chao Yu <chao@kernel.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>