net: ipa: heed napi_complete() return value

Pay attention to the return value of napi_complete(), completing
polling only if it returns true.

Just use napi rather than &channel->napi as the argument passed to
napi_complete().

Signed-off-by: Alex Elder <elder@linaro.org>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>