scsi: sr: Fix spelling mistake "does'nt" -> "doesn't"

There is a spelling mistake in a literal string. Fix it.

Link: https://lore.kernel.org/r/20210826115714.11844-1-colin.king@canonical.com


Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>