USB: diag_bridge: Fix a possible freed memory access

The platform device is freed in disconnect.  Don't access pdev
in diag_bridge_delete() which gets called after disconnect. Store
pdev->id in the corresponding driver's private structure.

CRs-Fixed: 470151
Change-Id: I2d97b508f227d6ccc3a87e03481293fa1054bbbc
Signed-off-by: Pavankumar Kondeti <pkondeti@codeaurora.org>