fs: dlm: remove additional dereference of lksb

This patch removes a dereference of lksb of lkb when calling ast
tracepoint. First it reduces additional overhead, even if traces
are not active. Second we can deference it in TP_fast_assign from
the existing lkb parameter.

Signed-off-by: Alexander Aring <aahringo@redhat.com>
Signed-off-by: David Teigland <teigland@redhat.com>