ide-cd: Don't warn on bogus block size unless it actually matters.

Frans Pop reported that his CDROM drive reports a blocksize of 2352,
and this causes new warnings due to commit
e8e7b9eb

 ("ide-cd: fix oops when using
growisofs").

What we're trying to do is make sure that "blocklen >> SECTOR_BITS"
is something the block layer won't choke on.

And for Frans' case "2352 >> SECTOR_BITS" is equal to
"2048 >> SECTOR_BITS", and thats "4".

So warning in this case gives no real benefit.

Reported-by: Frans Pop <elendil@planet.nl>
Tested-by: Frans Pop <elendil@planet.nl>
Signed-off-by: David S. Miller <davem@davemloft.net>