s390/dasd: remove unnecessary condition check

kmem_cache_destroy() can handle NULL pointer correctly, so there is
no need to check NULL pointer before calling kmem_cache_destroy().
Signed-off-by: Chengguang Xu <cgxu519@gmx.com>
Signed-off-by: Jan Höppner <hoeppner@linux.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

drivers/s390/block/dasd.c

@@ -3309,10 +3309,8 @@ dasd_exit(void)
 	dasd_proc_exit();
 #endif
 	dasd_eer_exit();
-        if (dasd_page_cache != NULL) {
-		kmem_cache_destroy(dasd_page_cache);
-		dasd_page_cache = NULL;
-	}
+	kmem_cache_destroy(dasd_page_cache);
+	dasd_page_cache = NULL;
 	dasd_gendisk_exit();
 	dasd_devmap_exit();
 	if (dasd_debug_area != NULL) {