V4L/DVB (8509): pvrusb2: fix device descriptions for HVR-1900 & HVR-1950

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