f2fs: remove an unneeded kfree(NULL)

This kfree() is no longer needed after a79dc083d7 "f2fs: move
bio_private allocation out of f2fs_bio_alloc()".  The "bio->bi_private"
is NULL here so it's a no-op.
Signed-off-by: NDan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: NJaegeuk Kim <jaegeuk.kim@samsung.com>

fs/f2fs/data.c

@@ -390,7 +390,6 @@ int f2fs_readpage(struct f2fs_sb_info *sbi, struct page *page,
 	bio->bi_end_io = read_end_io;
 
 	if (bio_add_page(bio, page, PAGE_CACHE_SIZE, 0) < PAGE_CACHE_SIZE) {
-		kfree(bio->bi_private);
 		bio_put(bio);
 		up_read(&sbi->bio_sem);
 		f2fs_put_page(page, 1);