fix a install bug and rename debug_fs* to apropriate names.

stage2/fsys_ffs.c

@@ -161,13 +161,13 @@ ffs_read (char *buf, int len)
 	size = len;
 
 #ifndef STAGE1_5
-      debug_fs_func = debug_fs;
+      disk_read_func = disk_read_hook;
 #endif /* STAGE1_5 */
 
       devread (fsbtodb (SUPERBLOCK, map), off, size, buf);
 
 #ifndef STAGE1_5
-      debug_fs_func = NULL;
+      disk_read_func = NULL;
 #endif /* STAGE1_5 */
 
       buf += size;