drbd: check on CONFIG_LBDAF, not LBD

It is called LBDAF since 2.6.31.

impact:
without this change, on 32bit,
DRBD would wrongly claim to only support 2TiB devices.
Signed-off-by: Lars Ellenberg <lars.ellenberg@linbit.com>
Signed-off-by: Philipp Reisner <philipp.reisner@linbit.com>

drivers/block/drbd/drbd_int.h

@@ -1275,7 +1275,7 @@ struct bm_extent {
 #if DRBD_MAX_SECTORS_BM < DRBD_MAX_SECTORS_32
 #define DRBD_MAX_SECTORS      DRBD_MAX_SECTORS_BM
 #define DRBD_MAX_SECTORS_FLEX DRBD_MAX_SECTORS_BM
-#elif !defined(CONFIG_LBD) && BITS_PER_LONG == 32
+#elif !defined(CONFIG_LBDAF) && BITS_PER_LONG == 32
 #define DRBD_MAX_SECTORS      DRBD_MAX_SECTORS_32
 #define DRBD_MAX_SECTORS_FLEX DRBD_MAX_SECTORS_32
 #else