V4L/DVB (5278): Bt8xx/: possible cleanups

This patch contains the following possible cleanups:
- remove the following unused global functions:
  - bttv-if.c: bttv_get_cardinfo()
  - bttv-if.c: bttv_get_id()
  - bttv-if.c: bttv_get_gpio_queue()
  - bttv-if.c: bttv_i2c_call()
- remove the following unused EXPORT_SYMBOL's:
  - bttv-gpio.c: bttv_sub_bus_type
  - bttv-gpio.c: bttv_gpio_inout
  - bttv-gpio.c: bttv_gpio_read
  - bttv-gpio.c: bttv_gpio_write
  - bttv-gpio.c: bttv_gpio_bits

Signed-off-by: Adrian Bunk <bunk@stusta.de>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>