Documentation/cdrom: fix German sharp s in LaTex

Apparently the LaTex abbreviation for the German "sharp s" (ß)
(Unicode U+00DF) has changed from {\sz} to {\ss}.  With {\sz},
I get this error at line 1016 (line number after another patch):

! Undefined control sequence.
l.1016 ...nel~2.0.  Further thanks to Heiko Ei{\sz
                                                  }feldt,

This is fixed by changing the {\sz} to {\ss}.

Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>