msm: ipa3: remove ul_dl sync from IPA MHI

Remove the usage of ul_dl_sync field in IPA MHI driver as this
is no longer in use.

CRs-Fixed: 990233
Change-Id: I7295da05664e72aa1b9120f7bc475f92addc095b
Acked-by: Ady Abraham <adya@qti.qualcomm.com>
Signed-off-by: Skylar Chang <chiaweic@codeaurora.org>