ocfs2: remove unnecessary NULL check before unregister_sysctl_table()

unregister_sysctl_table() checks for NULL pointers internally.  Remove
unneeded NULL check here.

Link: https://lkml.kernel.org/r/20250422073051.1334310-1-nichen@iscas.ac.cn


Signed-off-by: Chen Ni <nichen@iscas.ac.cn>
Reviewed-by: Joseph Qi <joseph.qi@linux.alibaba.com>
Cc: Mark Fasheh <mark@fasheh.com>
Cc: Joel Becker <jlbec@evilplan.org>
Cc: Junxiao Bi <junxiao.bi@oracle.com>
Cc: Changwei Ge <gechangwei@live.cn>
Cc: Jun Piao <piaojun@huawei.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>