V4L/DVB (13497): pvrusb2: Shorten device hardware description text to work around V4L shortcoming

The device text description in pvrusb2-devattr.c get mapped into a V4L
API string field that is unfortunately shorter than I expected.  No
sense fighting City Hall here - this change shortens the descriptions
to fit the limit.

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