staging: erofs: unzip_vle_lz4.c,utils.c: rectify BUG_ONs

remove all redundant BUG_ONs, and turn the rest
useful usages to DBG_BUGONs.

Signed-off-by: Gao Xiang <[e-mail]>
Reviewed-by: Chao Yu <[e-mail]>
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/staging/erofs/unzip_vle_lz4.c

···
 			if (compressed_pages[j] != page)
 				continue;
 
-			BUG_ON(mirrored[j]);
+			DBG_BUGON(mirrored[j]);
 			memcpy(percpu_data + j * PAGE_SIZE, dst, PAGE_SIZE);
 			mirrored[j] = true;
 			break;

drivers/staging/erofs/utils.c

···
 		list_del(&page->lru);
 	} else {
 		page = alloc_pages(gfp | __GFP_NOFAIL, 0);
-
-		BUG_ON(page == NULL);
-		BUG_ON(page->mapping != NULL);
 	}
 	return page;
 }
···
 		/* decrease refcount added by erofs_workgroup_put */
 		if (unlikely(oldcount == 1))
 			atomic_long_dec(&erofs_global_shrink_cnt);
-		BUG_ON(index != grp->index);
+		DBG_BUGON(index != grp->index);
 	}
 	rcu_read_unlock();
 	return grp;
···
 	struct erofs_sb_info *sbi;
 	int err;
 
-	/* grp->refcount should not < 1 */
-	BUG_ON(!atomic_read(&grp->refcount));
+	/* grp shouldn't be broken or used before */
+	if (unlikely(atomic_read(&grp->refcount) != 1)) {
+		DBG_BUGON(1);
+		return -EINVAL;
+	}
 
 	err = radix_tree_preload(GFP_NOFS);
 	if (err)