scsi: sd: make sd_devt_release() static

Fixes the following sparse warning:

drivers/scsi/sd.c:3087:6: warning:
 symbol 'sd_devt_release' was not declared. Should it be static?
Signed-off-by: Wei Yongjun <weiyongjun1@huawei.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

drivers/scsi/sd.c

@@ -3084,7 +3084,7 @@ struct sd_devt {
 	struct disk_devt disk_devt;
 };
 
-void sd_devt_release(struct disk_devt *disk_devt)
+static void sd_devt_release(struct disk_devt *disk_devt)
 {
 	struct sd_devt *sd_devt = container_of(disk_devt, struct sd_devt,
 			disk_devt);