[PATCH] fix cdrom mt rainier probe

[PATCH] fix cdrom mt rainier probe

Writing to RAM capable media was broken by the moving of write flag
detection from probe to drive open time.  The media would stay
terminally RO due to the set_disk_ro() call.

This fixes the code to do the right thing - the detection stays at open
time (which it must, since it depends on the media), and we fail with
-EROFS if the media can't be written.

Signed-off-by: Jens Axboe <axboe@suse.de>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>