Logfs: Allow NULL block_isbad() methods

Not all mtd drivers define block_isbad().  Let's assume no bad blocks
instead of refusing to mount.
Signed-off-by: NJoern Engel <joern@logfs.org>

fs/logfs/dev_mtd.c

@@ -150,15 +150,14 @@ static struct page *mtd_find_first_sb(struct super_block *sb, u64 *ofs)
 	filler_t *filler = mtd_readpage;
 	struct mtd_info *mtd = super->s_mtd;
 
-	if (!mtd->block_isbad)
-		return NULL;
-
 	*ofs = 0;
+	if (mtd->block_isbad) {
 		while (mtd->block_isbad(mtd, *ofs)) {
 			*ofs += mtd->erasesize;
 			if (*ofs >= mtd->size)
 				return NULL;
 		}
+	}
 	BUG_ON(*ofs & ~PAGE_MASK);
 	return read_cache_page(mapping, *ofs >> PAGE_SHIFT, filler, sb);
 }
@@ -170,15 +169,14 @@ static struct page *mtd_find_last_sb(struct super_block *sb, u64 *ofs)
 	filler_t *filler = mtd_readpage;
 	struct mtd_info *mtd = super->s_mtd;
 
-	if (!mtd->block_isbad)
-		return NULL;
-
 	*ofs = mtd->size - mtd->erasesize;
+	if (mtd->block_isbad) {
 		while (mtd->block_isbad(mtd, *ofs)) {
 			*ofs -= mtd->erasesize;
 			if (*ofs <= 0)
 				return NULL;
 		}
+	}
 	*ofs = *ofs + mtd->erasesize - 0x1000;
 	BUG_ON(*ofs & ~PAGE_MASK);
 	return read_cache_page(mapping, *ofs >> PAGE_SHIFT, filler, sb);