V4L/DVB (7893): xc5000: bug-fix: allow multiple devices in a single system

The current code passes a context pointer in the xc5000_config struct.
This context pointer is used in the tuner_callback function, used to
reset the device after firmware download.

The xc5000_config struct is a static structure, whose .priv member was
being assigned before calling xc5000_attach().  If there are more than
one of the same device type installed on a single system, the last one
to assign xc5000_config.priv will "win", and all others will cease to
function properly.

This patch passes the context pointer in xc5000_attach() rather that
storing it within the static struct xc5000_config.

Signed-off-by: Michael Krufky <mkrufky@linuxtv.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>