[JFFS2] Correct cleanmarker checks -- we should use only 8 bytes

Commit a7a6ace1 revamped the OOB
handling but accidentally switched to 12-byte cleanmarkers, which is
incompatible with what 'flash_eraseall -j' will do. So using
flash_eraseall -j and then trying to mount the 'empty' flash will fail,
because the cleanmarkers aren't recognised.
Signed-off-by: NDavid Woodhouse <dwmw2@infradead.org>

fs/jffs2/wbuf.c

@@ -1008,8 +1008,8 @@ int jffs2_flash_read(struct jffs2_sb_info *c, loff_t ofs, size_t len, size_t *re
 
 #define NR_OOB_SCAN_PAGES 4
 
-/* For historical reasons we use only 12 bytes for OOB clean marker */
-#define OOB_CM_SIZE 12
+/* For historical reasons we use only 8 bytes for OOB clean marker */
+#define OOB_CM_SIZE 8
 
 static const struct jffs2_unknown_node oob_cleanmarker =
 {