time: Use ARRAY_SIZE macro in timecompare.c

Replace sizeof(buffer)/sizeof(buffer[0]) with ARRAY_SIZE(buffer) in
kernel/time/timecompare.c

Signed-off-by: Nikitas Angelinas <nikitasangelinas@googlemail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>