media: dw2102: make dvb_usb_device_description structures const

dvb_usb_device_description structures are only used during a copy
operation. Therefore, declare them as const.

Signed-off-by: Bhumika Goyal <bhumirks@gmail.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>