msm: ipa3: fix hdr offset issue

Hdr offset calculation is wrong when
driver received clean-up ioctl from
user-space. The fix is to find right
hdr offset to commit ned headers.

Change-Id: I70878a19b64c3defa6101bd68d435f0b74bcfb9b
Signed-off-by: Skylar Chang <chiaweic@codeaurora.org>