ieee1394: sbp2: fix probing of some DVD-ROM/RWs

Since commit 98e238cd

 in Linux 2.6.19,
"ieee1394: sbp2: don't prefer MODE SENSE 10", some FireWire DVD-ROMs and
DVD-RWs were mistaken as CD-ROM because sr_mod now sent MODE SENSE 6.
The MMC command set includes only MODE SENSE 10.
http://bugzilla.kernel.org/show_bug.cgi?id=7800

This fix lets sbp2 switch scsi_device.use_10_for_rw on for MMC LUs.
This should rather be done in the command set driver sr_mod, not in the
sbp2 transport driver, and an according patch will follow for a next
Linux release.

Signed-off-by: Stefan Richter <stefanr@s5r6.in-berlin.de>