UBI: block: Add CONFIG_BLOCK dependency

The UBI block driver depends on the block infrastructure. Add the
proper dependency and fix a build error when CONFIG_BLOCK is not selected.
Reported-by: Nkbuild test robot <fengguang.wu@intel.com>
Signed-off-by: NEzequiel Garcia <ezequiel.garcia@free-electrons.com>
Signed-off-by: NArtem Bityutskiy <artem.bityutskiy@linux.intel.com>

drivers/mtd/ubi/Kconfig

@@ -90,6 +90,7 @@ config MTD_UBI_GLUEBI
 config MTD_UBI_BLOCK
 	bool "Read-only block devices on top of UBI volumes"
 	default n
+	depends on BLOCK
 	help
 	   This option enables read-only UBI block devices support. UBI block
 	   devices will be layered on top of UBI volumes, which means that the