msm: ipa: fix data stall due to NAPI poll

In some cases, napi poll function will stop polling
even if there are more packets to process. This may lead
to a data stall where there are packets to process from IPA
but IPA driver does not process those. This change ensures that
as long as there is data to read from IPA, napi poll will be called.

Change-Id: Id2c218e15229717ea30e4bef04e32a94371f2113
CRs-Fixed: 2120691
Acked-by: Ady Abraham <adya@qti.qualcomm.com>
Signed-off-by: Skylar Chang <chiaweic@codeaurora.org>