f2fs: fix wrong condition check
f2fs: fix wrong condition check

While an orphan inode has zero link_count, f2fs_gc is able to select the inode
for foreground gc.

- f2fs_gc
 - do_garbage_collect
   - gc_data_segment
     : f2fs_iget is failed
     : get_valid_blocks() != 0, so that retry
--> here we got the infinite loop.

This patch resolved this issue.

Signed-off-by: Jaegeuk Kim <20424effba9d4aeeb410130c5f23aa328fa29e09@samsung.com>

KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs