Bluetooth: kill all the anchored URBs on USB device disconnect

When USB driver is unloaded (rmmod), kill all the URBs before
freeing up various data structs. If not done, URB callback might
lead to NULL pointer dereference or page fault.

Change-Id: Id719f090ae96845fac50b2d97dc7e698f39b5ce5
Signed-off-by: Rupesh Tatiya <rtatiya@codeaurora.org>