[MTD] [NAND] Correct misspelled preprocessor variable.

Replace the apparently misspelled preprocessor variable
"MTD_NAND_DISKONCHIP_BBTWRITE" with the correct form
"CONFIG_MTD_NAND_DISKONCHIP_BBTWRITE".
Signed-off-by: NRobert P. J. Day <rpjday@mindspring.com>
Signed-off-by: NDavid Woodhouse <dwmw2@infradead.org>

drivers/mtd/nand/diskonchip.c

@@ -114,7 +114,7 @@ module_param(no_autopart, int, 0);
 static int show_firmware_partition = 0;
 module_param(show_firmware_partition, int, 0);
 
-#ifdef MTD_NAND_DISKONCHIP_BBTWRITE
+#ifdef CONFIG_MTD_NAND_DISKONCHIP_BBTWRITE
 static int inftl_bbt_write = 1;
 #else
 static int inftl_bbt_write = 0;