media: pvrusb2: use a different format for warnings

When the pvrusb2 driver detects that there's something wrong with the
device, it prints a warning message. Right now those message are
printed in two different formats:

1. ***WARNING*** message here
2. WARNING: message here

There's an issue with the second format. Syzkaller recognizes it as a
message produced by a WARN_ON(), which is used to indicate a bug in the
kernel. However pvrusb2 prints those warnings to indicate an issue with
the device, not the bug in the kernel.

This patch changes the pvrusb2 driver to consistently use the first
warning message format. This will unblock syzkaller testing of this
driver.

Reported-by:  <syzbot+af8f8d2ac0d39b0ed3a0@syzkaller.appspotmail.com>
Reported-by:  <syzbot+170a86bf206dd2c6217e@syzkaller.appspotmail.com>
Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>