mtd: introduce mtd_block_isbad interface

Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>
diff --git a/drivers/mtd/tests/mtd_speedtest.c b/drivers/mtd/tests/mtd_speedtest.c
index c7b18e1..ecb2878 100644
--- a/drivers/mtd/tests/mtd_speedtest.c
+++ b/drivers/mtd/tests/mtd_speedtest.c
@@ -296,7 +296,7 @@
 	loff_t addr = ebnum * mtd->erasesize;
 	int ret;
 
-	ret = mtd->block_isbad(mtd, addr);
+	ret = mtd_block_isbad(mtd, addr);
 	if (ret)
 		printk(PRINT_PREF "block %d is bad\n", ebnum);
 	return ret;