staging/lustre/osc: fixed a typo in osc_cache_truncate_start

Dump osc_extent waiting instead of ext in case error occurred.

Intel-bug-id: https://jira.hpdd.intel.com/browse/LU-3359
Lustre-change: http://review.whamcloud.com/6402
Signed-off-by: Jinshan Xiong <jinshan.xiong@intel.com>
Reviewed-by: Lai Siyao <lai.siyao@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>
Signed-off-by: Peng Tao <tao.peng@emc.com>
Signed-off-by: Andreas Dilger <andreas.dilger@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/lustre/lustre/osc/osc_cache.c

@@ -2699,7 +2699,7 @@ again:
 		 * should take care of it. */
 		rc = osc_extent_wait(env, waiting, OES_INV);
 		if (rc < 0)
-			OSC_EXTENT_DUMP(D_CACHE, ext, "wait error: %d.\n", rc);
+			OSC_EXTENT_DUMP(D_CACHE, waiting, "error: %d.\n", rc);
 
 		osc_extent_put(env, waiting);
 		waiting = NULL;