f2fs: cleanup the f2fs_bio_alloc routine

Do cleanup more for better code readability.

- Change the parameter set of f2fs_bio_alloc()
  This function should allocate a bio only since it is not something like
  f2fs_bio_init(). Instead, the caller should initialize the allocated bio.

- Introduce SECTOR_FROM_BLOCK
  This macro translates a block address to its sector address.

Signed-off-by: Jaegeuk Kim <jaegeuk.kim@samsung.com>
Reviewed-by: Namjae Jeon <namjae.jeon@samsung.com>

fs/f2fs/data.c

@@ -343,11 +343,12 @@ int f2fs_readpage(struct f2fs_sb_info *sbi, struct page *page,
 	down_read(&sbi->bio_sem);
 
 	/* Allocate a new bio */
-	bio = f2fs_bio_alloc(bdev, blk_addr << (sbi->log_blocksize - 9),
-				1, GFP_NOFS | __GFP_HIGH);
+	bio = f2fs_bio_alloc(bdev, 1);
 
 	/* Initialize the bio */
+	bio->bi_sector = SECTOR_FROM_BLOCK(sbi, blk_addr);
 	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);