f2fs: Fix the race condition of resize flag between resizefs

Because the set/clear SBI_IS_RESIZEFS flag not between any locks,
In the following case:
  thread1			thread2
   ->ioctl(resizefs)
    ->set RESIZEFS flag		 ->ioctl(resizefs)
    ...                   	  ->set RESIZEFS flag
    ->clear RESIZEFS flag
    				  ->resizefs stream
				    # No RESIZEFS flag in the stream

Also before freeze_super, the resizefs not started, we should not set
the SBI_IS_RESIZEFS flag.

So move the set/clear SBI_IS_RESIZEFS flag between the cp_mutex and
gc_lock.

Fixes: b4b10061 ("f2fs: refactor resize_fs to avoid meta updates in progress")
Signed-off-by: Zhang Xiaoxu <zhangxiaoxu5@huawei.com>
Signed-off-by: Zhang Qilong <zhangqilong3@huawei.com>
Reviewed-by: Chao Yu <chao@kernel.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>