net: ipa: kill ipa_clock_get_additional()

Now that ipa_clock_get_additional() is a trivial wrapper around
pm_runtime_get_if_active(), just open-code it in its only caller
and delete the function.

Signed-off-by: Alex Elder <elder@linaro.org>
Signed-off-by: David S. Miller <davem@davemloft.net>