This patch fixes problems(kernel oopses) with unplug of device while
it's working.
Patch adds disconnect_lock mutex, changes usb_amradio_close and
usb_amradio_disconnect functions and adds a lot of safety checks.
Signed-off-by: Alexey Klimov <klimov.linux@gmail.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>