dlm: trivial annotation of be16 value

fs/dlm/dir.c:419:14: warning: incorrect type in assignment (different base types)
fs/dlm/dir.c:419:14:    expected unsigned short [unsigned] [addressable] [assigned] [usertype] be_namelen
fs/dlm/dir.c:419:14:    got restricted __be16 [usertype] <noident>

Signed-off-by: Harvey Harrison <harvey.harrison@gmail.com>
Signed-off-by: David Teigland <teigland@redhat.com>