f2fs: avoid stale fi->gdirty_list pointer

When doing fault injection test, f2fs_evict_inode() didn't remove gdirty_list
which incurs a kernel panic due to wrong pointer access.

Reviewed-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>