ocfs2/cluster: dereferencing before checking in nst_seq_show()

In the original code, we dereferenced "nst" before checking that it was
non-NULL.  I moved the check forward and pulled the code in an indent
level.

Signed-off-by: Dan Carpenter <error27@gmail.com>
Signed-off-by: Joel Becker <joel.becker@oracle.com>