net: ipa: pass a platform device to ipa_smp2p_init()

Rather than using the platform device pointer field in the IPA
pointer, pass a platform device pointer to ipa_smp2p_init().  Use
that pointer throughout that function.

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