V4L/DVB (13223): pvrusb2: Soften encoder warning message

pvrusb2: Encoder failures are mostly recoverable by the driver.  While
it would sure be nice not to have the failure happen in the first
place, this has been going on for years and I doubt that a real
solution will ever present itself.  I think that part's firmware is
just slightly flakey and we have to deal with it.  The driver does
deal with it just fine, but the warning message going into the kernel
log is probably a little more alarming than it should be.  So try to
soften up the warning somewhat.

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