mtd: Correct dependency of BLK

In the case of MTD_BLOCK and UBI_BLOCK they should be select'ing BLK as
they provide block device functionality and not depending on some other
block device already being enabled too (as is the typical case).

Reviewed-by: Quentin Schulz <quentin.schulz@cherry.de>
Reviewed-by: Peter Robinson <pbrobinson@gmail.com>
Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/drivers/mtd/Kconfig b/drivers/mtd/Kconfig
index c71c1e5..185e834 100644
--- a/drivers/mtd/Kconfig
+++ b/drivers/mtd/Kconfig
@@ -34,7 +34,7 @@
 
 config MTD_BLOCK
 	bool "Enable block device access to MTD devices"
-	depends on BLK
+	select BLK
 	help
 	  Enable support for block device access to MTD devices
 	  using blk_ops abstraction.