ubifs: Correct the total block count by deducting journal reservation

Since commit e874dcd ("ubifs: Reserve one leb for each journal
head while doing budget"), available space is calulated by deducting
reservation for all journal heads. However, the total block count (
which is only used by statfs) is not updated yet, which will cause
the wrong displaying for used space(total - available).
Fix it by deducting reservation for all journal heads from total
block count.

Fixes: e874dcd ("ubifs: Reserve one leb for each journal head while doing budget")
Signed-off-by: Zhihao Cheng <chengzhihao1@huawei.com>
Signed-off-by: Richard Weinberger <richard@nod.at>

fs/ubifs/super.c

@@ -773,10 +773,10 @@ static void init_constants_master(struct ubifs_info *c)
 	 * necessary to report something for the 'statfs()' call.
 	 *
 	 * Subtract the LEB reserved for GC, the LEB which is reserved for
-	 * deletions, minimum LEBs for the index, and assume only one journal
-	 * head is available.
+	 * deletions, minimum LEBs for the index, the LEBs which are reserved
+	 * for each journal head.
 	 */
-	tmp64 = c->main_lebs - 1 - 1 - MIN_INDEX_LEBS - c->jhead_cnt + 1;
+	tmp64 = c->main_lebs - 1 - 1 - MIN_INDEX_LEBS - c->jhead_cnt;
 	tmp64 *= (long long)c->leb_size - c->leb_overhead;
 	tmp64 = ubifs_reported_space(c, tmp64);
 	c->block_cnt = tmp64 >> UBIFS_BLOCK_SHIFT;