wimax: fix kernel-doc for debufs_dentry member of struct wimax_dev

Reported by Randy Dunlap from a warning in the v2.6.29 merge window
tree as of 2009/1/8.

Signed-off-by: Inaky Perez-Gonzalez <inaky@linux.intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>