[PATCH] enable device mapper in compat layer

The compat ioctls for device mapper were not being enabled due to an
incorrect config option.

include/linux/compat_ioctl.h

@@ -117,7 +117,7 @@ COMPATIBLE_IOCTL(START_ARRAY)
 COMPATIBLE_IOCTL(STOP_ARRAY)
 COMPATIBLE_IOCTL(STOP_ARRAY_RO)
 COMPATIBLE_IOCTL(RESTART_ARRAY_RW)
-#ifdef CONFIG_DM
+#ifdef CONFIG_BLK_DEV_DM
 /* DM */
 COMPATIBLE_IOCTL(DM_VERSION)
 COMPATIBLE_IOCTL(DM_REMOVE_ALL)