i40iw: Fix sequence number for the first partial FPDU

Partial FPDU processing is broken as the sequence number
for the first partial FPDU is wrong due to incorrect
Q2 buffer offset. The offset should be 64 rather than 16.

Fixes: 786c6adb

 ("i40iw: add puda code")
Signed-off-by: Shiraz Saleem <shiraz.saleem@intel.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>