[S390] dcss: fix build bug.

Fix this compile bug:

  CC      drivers/s390/block/dcssblk.o
drivers/s390/block/dcssblk.c: In function 'dcssblk_add_store':
drivers/s390/block/dcssblk.c:387: error: implicit declaration of function 'dcssblk_get_segment_by_name'
drivers/s390/block/dcssblk.c:389: error: label 'release_gd' used but not defined
make[1]: *** [drivers/s390/block/dcssblk.o] Error 1
make: *** [drivers/s390/block/] Error 2

Cc: Gerald Schaefer <gerald.schaefer@de.ibm.com>
Signed-off-by: NHeiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: NMartin Schwidefsky <schwidefsky@de.ibm.com>

drivers/s390/block/dcssblk.c

@@ -384,9 +384,10 @@ dcssblk_add_store(struct device *dev, struct device_attribute *attr, const char
 	 * get minor, add to list
 	 */
 	down_write(&dcssblk_devices_sem);
-	if (dcssblk_get_segment_by_name(local_buf)) {
+	if (dcssblk_get_device_by_name(local_buf)) {
+		up_write(&dcssblk_devices_sem);
 		rc = -EEXIST;
-		goto release_gd;
+		goto unload_seg;
 	}
 	rc = dcssblk_assign_free_minor(dev_info);
 	if (rc) {