net: ipa: get rid of extra clock reference

Suspending the IPA hardware is now managed by the runtime PM core
code.  The ->runtime_idle callback returns a non-zero value, so it
will never suspend except when forced.  As a result, there's no need
to take an extra "do not suspend" clock reference.

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