V4L/DVB (5366): Pvrusb2: Fix compilation warning for amd64 builds (use %zu instead of %u)

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