sr: simplify the local variable initialization in sr_block_open()

Commit 01d0c698 ("sr: implement ->free_disk to simplify refcounting")
refactored sr_block_open(), initialized one variable with a duplicate
assignment (probably an unintended copy & paste duplication) and turned one
error case into an early return, which makes the initialization of the
return variable needless.

So, simplify the local variable initialization in sr_block_open() to make
the code a bit more clear.

No functional change. No change in resulting object code.
Signed-off-by: NLukas Bulwahn <lukas.bulwahn@gmail.com>
Reviewed-by: NChristoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20220314150321.17720-1-lukas.bulwahn@gmail.comSigned-off-by: NJens Axboe <axboe@kernel.dk>

drivers/scsi/sr.c

@@ -483,9 +483,9 @@ static void sr_revalidate_disk(struct scsi_cd *cd)
 
 static int sr_block_open(struct block_device *bdev, fmode_t mode)
 {
-	struct scsi_cd *cd = cd = scsi_cd(bdev->bd_disk);
+	struct scsi_cd *cd = scsi_cd(bdev->bd_disk);
 	struct scsi_device *sdev = cd->device;
-	int ret = -ENXIO;
+	int ret;
 
 	if (scsi_device_get(cd->device))
 		return -ENXIO;