cirrus: cs89x0: fix time comparison

To be future-proof and for better readability the time comparisons are
modified to use time_before, time_after, and time_after_eq instead of
plain, error-prone math.

Signed-off-by: Asaf Vertz <asaf.vertz@tandemg.com>
Signed-off-by: David S. Miller <davem@davemloft.net>