f2fs: add f2fs_gc exception handle in f2fs_ioc_gc_range

f2fs: add f2fs_gc exception handle in f2fs_ioc_gc_range

When f2fs_ioc_gc_range performs multiple segments gc ops, the return
value of f2fs_ioc_gc_range is determined by the last segment gc ops.
If its ops failed, the f2fs_ioc_gc_range will be considered to be failed
despite some of previous segments gc ops succeeded. Therefore, so we
fix: Redefine the return value of getting victim ops and add exception
handle for f2fs_gc. In particular, 1).if target has no valid block, it
will go on. 2).if target sectoion has valid block(s), but it is current
section, we will reminder the caller.

Signed-off-by: Qilong Zhang <zhangqilong3@huawei.com>
Reviewed-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>