Fix sparse build warning:

lib/test_lockup.c:403:1: warning:
 symbol '__pcpu_scope_test_works' was not declared. Should it be static?
Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Wei Yongjun <weiyongjun1@huawei.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Link: http://lkml.kernel.org/r/20200707112252.9047-1-weiyongjun1@huawei.comSigned-off-by: Linus Torvalds <torvalds@linux-foundation.org>