drivers/cdrom/cdrom.c: relax check on dvd manufacturer value

The report has an ISO which has a very long manufacturer ID.  It seems
that Linux is wrong, not the ISO maker.

Relax the check for the length of this field: emit a warning and truncate
the incoming data to 2048 bytes rather than rejecting the entire thing.

dvd_manufact.value isn't null-terminated.  I'm not even sure if it's a
string.  The kernel doesn't apepar to use it anyway.

Addresses https://bugzilla.kernel.org/show_bug.cgi?id=39062



Reported-by:  <ale.goujon@gmail.com>
Tested-by:  <ale.goujon@gmail.com>
Cc: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Jens Axboe <jaxboe@fusionio.com>