[media] media: get rid of unused "extra_links" param on media_entity_init()

Currently, media_entity_init() creates an array with the links,
allocated at init time. It provides a parameter (extra_links)
that would allocate more links than the current needs, but this
is not used by any driver.

As we want to be able to do dynamic link allocation/removal,
we'll need to change the implementation of the links. So,
before doing that, let's first remove that extra unused
parameter, in order to cleanup the interface first.

Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>
Acked-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Acked-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>

Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>