V4L/DVB (6580): Set slave's master before master's attach call.

V4L: Int if: Set slave's master before attach, remove master argument

The master also now gets its own pointer from slave's structure.

Signed-off-by: Sakari Ailus <sakari.ailus@nokia.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>