[media] pvrusb2: use KERNEL_CONT where needed

Some continuation messages are not using KERNEL_CONT.

Since commit 56387331 ("Merge branch 'printk-cleanups"),
this won't work as expected anymore. So, let's add KERN_CONT
to those lines.

Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>