mtd: of_parts: fix breakage in Kconfig

MTD_OF_PARTS and the default setting is not working due to using 'Y'
instead of 'y', introduced in commit
d6137bad. This made our board, and
possibly other boards using DTS defined partitions and not having
CONFIG_MTD_OF_PARTS=y defined in the defconfig, fail to mount root.
Signed-off-by: NFrank Svendsboe <frank.svendsboe@gmail.com>
Cc: stable@kernel.org [3.2+]
Signed-off-by: NArtem Bityutskiy <artem.bityutskiy@linux.intel.com>
Signed-off-by: NDavid Woodhouse <David.Woodhouse@intel.com>

drivers/mtd/Kconfig

@@ -128,7 +128,7 @@ config MTD_AFS_PARTS
 
 config MTD_OF_PARTS
 	tristate "OpenFirmware partitioning information support"
-	default Y
+	default y
 	depends on OF
 	help
 	  This provides a partition parsing function which derives