imx_sdp: keep track of the buffer's file offset
imx_sdp: keep track of the buffer's file offset

Signed-off-by: Troy Kisky <debfc29e3a9e989b865b88f1f207951588bac6b3@boundarydevices.com>

boundarydevices/imx_usb_loader,bwalle/imx_usb_loader