V4L/DVB (9276): videobuf-dvb: two functions are now static

This patch marks those two functions as static:
	static int videobuf_dvb_register_adapter(struct videobuf_dvb_frontends *fe,
	static int videobuf_dvb_register_frontend(struct dvb_adapter *adapter,

Since MFE patches changed their calls by videobuf_dvb_register_bus.

To avoid having to declare the prototypes, the patch moves
videobuf_dvb_register_bus() to be after the declaration of the above functions
used there.

Cc: Steven Toth <stoth@linuxtv.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>