V4L/DVB (6335): cx8802: Replace list_for_each+list_entry with list_for_each_entry

Less code and more efficient.

Got ride of a variable that counted the number of devices in
cx8802_unregister_driver() but was never used.  Looked leftover from a
cut&paste.

Signed-off-by: Trent Piepho <xyzzy@speakeasy.org>
Reviewed-by: Michael Krufky <mkrufky@linuxtv.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>