net: ipa: disable clock in suspend

Disable the IPA clock rather than dropping a reference to it in the
system suspend callback.  This forces the suspend to occur without
affecting existing references.

Similarly, enable the clock rather than taking a reference in
ipa_resume(), forcing a resume without changing the reference count.

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