ocfs2: remove unneeded NULL check

In commit 1faf2894 ("ocfs2_dlm: disallow a domain join if node maps
mismatch") we introduced a new earlier NULL check so this one is not
needed.  Also static checkers complain because we dereference it first
and then check for NULL.

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Cc: Mark Fasheh <mfasheh@suse.com>
Cc: Joel Becker <jlbec@evilplan.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>