UPSTREAM: mlx4: include clocksource.h again

commit d9f393734af52b7b09f02439164cc7182e17063c upstream.

This driver uses the function, clocksource_khz2mult, and so it really must
include clocksource.h.

Signed-off-by: Richard Cochran <richardcochran@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Change-Id: I9d7769c54e30581331e75c58deef38791baef3e6
Signed-off-by: Amit Pundir <amit.pundir@linaro.org>