V4L/DVB (5940): Export v4l2_int_device_{, un}register

This patch fixes the following build error:

<--  snip  -->

...
  MODPOST 2135 modules
make[2]: *** [__modpost] Error 1

<--  snip  -->

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