net: ethernet: ti: cpts: drop excessive writes to CTRL and INT_EN regs

CPTS module and IRQs are always enabled when CPTS is registered,
before starting overflow check work, and disabled during
deregistration, when overflow check work has been canceled already.
So, It doesn't require to (re)enable CPTS module and IRQs in
cpts_overflow_check().

Signed-off-by: Grygorii Strashko <grygorii.strashko@ti.com>
Acked-by: Richard Cochran <richardcochran@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>