V4L/DVB: pvrusb2-v4l2: Rename dev_info to pdi

There is a macro called dev_info that prints struct device specific
information.  Having variables with the same name can be confusing and
prevents conversion of the macro to a function.

Rename the existing dev_info variables to something else in preparation
to converting the dev_info macro to a function.

Signed-off-by: Joe Perches <joe@perches.com>
Acked-by: Mike Isely <isely@pobox.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>