media: pvrusb2: Convert timers to use timer_setup()

In preparation for unconditionally passing the struct timer_list pointer to
all timer callbacks, switch to using the new timer_setup() and from_timer()
to pass the timer pointer explicitly.

Cc: Mike Isely <isely@pobox.com>
Cc: Mauro Carvalho Chehab <mchehab@kernel.org>
Cc: linux-media@vger.kernel.org
Signed-off-by: Kees Cook <keescook@chromium.org>
Acked-By: Mike Isely <isely@pobox.com>
Acked-by: Hans Verkuil <hans.verkuil@cisco.com>