cdrom: set default timeout to 7 seconds

It's a known fact that Windows times out commands after 7 seconds, so
drives generally try and respond if they can before that happens.  We
default to 5 seconds, which sometimes is a bit too short.

Jeremy Higdon reported here:

    http://lkml.org/lkml/2007/1/1/145



that his drive takes longer than 5 seconds for a "read track
information" command, later confirming that it is about 6.7 seconds.

So just do the sane thing and change the default command timeout to 7
seconds to avoid other surprises.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
Signed-off-by: Adrian Bunk <bunk@stusta.de>