selftests: timers: valid-adjtimex: build fix for newer toolchains

stable inclusion
from stable-v5.10.137
commit ee3cc4c7612143bfa731725180c42e58afb70c35
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I60PLB

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=ee3cc4c7612143bfa731725180c42e58afb70c35



--------------------------------

[ Upstream commit 9a162977 ]

Toolchains with an include file 'sys/timex.h' based on 3.18 will have a
'clock_adjtime' definition added, so it can't be static in the code:

valid-adjtimex.c:43:12: error: static declaration of ‘clock_adjtime’ follows non-static declaration

Fixes: e03a58c3 ("kselftests: timers: Add adjtimex SETOFFSET validity tests")
Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Acked-by: John Stultz <jstultz@google.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>
Reviewed-by: Wei Li <liwei391@huawei.com>