V4L/DVB (6696): pvrusb2: Miscellaneous tweaks for controlling tuner type and video standard

Correctly mark when a tuner type is set.  Report more faithfully
information about known supported device video standards.

Signed-off-by: Mike Isely <isely@pobox.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>