selftests: timers: fix declarations of main()

Mixing up argc/argv went unnoticed because they were not used. Still,
this is worth fixing.

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>