btrfs: extent_io: Kill the forward declaration of flush_write_bio

There is no need to forward declare flush_write_bio(), as it only
depends on submit_one_bio().  Both of them are pretty small, just move
them to kill the forward declaration.
Reviewed-by: Nikolay Borisov <nborisov@suse.com>
Reviewed-by: Johannes Thumshirn <jthumshirn@suse.de>
Signed-off-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/extent_io.c

@@ -147,7 +147,38 @@ static int add_extent_changeset(struct extent_state *state, unsigned bits,
 	return ret;
 }
 
-static void flush_write_bio(struct extent_page_data *epd);
+static int __must_check submit_one_bio(struct bio *bio, int mirror_num,
+				       unsigned long bio_flags)
+{
+	blk_status_t ret = 0;
+	struct bio_vec *bvec = bio_last_bvec_all(bio);
+	struct page *page = bvec->bv_page;
+	struct extent_io_tree *tree = bio->bi_private;
+	u64 start;
+
+	start = page_offset(page) + bvec->bv_offset;
+
+	bio->bi_private = NULL;
+
+	if (tree->ops)
+		ret = tree->ops->submit_bio_hook(tree->private_data, bio,
+					   mirror_num, bio_flags, start);
+	else
+		btrfsic_submit_bio(bio);
+
+	return blk_status_to_errno(ret);
+}
+
+static void flush_write_bio(struct extent_page_data *epd)
+{
+	if (epd->bio) {
+		int ret;
+
+		ret = submit_one_bio(epd->bio, 0, 0);
+		BUG_ON(ret < 0); /* -ENOMEM */
+		epd->bio = NULL;
+	}
+}
 
 int __init extent_io_init(void)
 {
@@ -2690,28 +2721,6 @@ struct bio *btrfs_bio_clone_partial(struct bio *orig, int offset, int size)
 	return bio;
 }
 
-static int __must_check submit_one_bio(struct bio *bio, int mirror_num,
-				       unsigned long bio_flags)
-{
-	blk_status_t ret = 0;
-	struct bio_vec *bvec = bio_last_bvec_all(bio);
-	struct page *page = bvec->bv_page;
-	struct extent_io_tree *tree = bio->bi_private;
-	u64 start;
-
-	start = page_offset(page) + bvec->bv_offset;
-
-	bio->bi_private = NULL;
-
-	if (tree->ops)
-		ret = tree->ops->submit_bio_hook(tree->private_data, bio,
-					   mirror_num, bio_flags, start);
-	else
-		btrfsic_submit_bio(bio);
-
-	return blk_status_to_errno(ret);
-}
-
 /*
  * @opf:	bio REQ_OP_* and REQ_* flags as one value
  * @tree:	tree so we can call our merge_bio hook
@@ -4005,17 +4014,6 @@ static int extent_write_cache_pages(struct address_space *mapping,
 	return ret;
 }
 
-static void flush_write_bio(struct extent_page_data *epd)
-{
-	if (epd->bio) {
-		int ret;
-
-		ret = submit_one_bio(epd->bio, 0, 0);
-		BUG_ON(ret < 0); /* -ENOMEM */
-		epd->bio = NULL;
-	}
-}
-
 int extent_write_full_page(struct page *page, struct writeback_control *wbc)
 {
 	int ret;