r311977: kernel build failure when NANDFS in kernel

On r311977, buildkernel fails with the error shown below. Kernel ist
customised and "options NANDFS" has been added as well as "device nand"
- the error shown suggest that is has to do with NANDFS.


 [...]
===> cc/cc_cdg (all)
--- nand_geom.o ---
/usr/src/sys/dev/nand/nand_geom.c:419:2: error: must use 'struct' tag
to refer to type 'disk' disk->d_rotation_rate = DISK_RR_NON_ROTATING;
        ^
        struct 
/usr/src/sys/dev/nand/nand_geom.c:419:6: error: expected identifier or
'(' disk->d_rotation_rate = DISK_RR_NON_ROTATING;
            ^
2 errors generated.
*** [nand_geom.o] Error code 1