msm: ipa: fix IPA MHI unit tests

Connect a test producer pipe for MHI unit tests as the
default LAN_PROD pipe is not connected on MHI config.

Change-Id: I2fc1ff8758d222a738d570b5babc22ced2b43219
CRs-Fixed: 2066878
Acked-by: Ady Abraham <adya@qti.qualcomm.com>
Signed-off-by: Skylar Chang <chiaweic@codeaurora.org>