libata: Initialize qc->pad_len

Initialize qc->pad_len for each new command. This ensures
that pad_len is not set to a stale value for zero data
length commands.

Signed-off-by: Brian King <brking@linux.vnet.ibm.com>
Signed-off-by: Jeff Garzik <jeff@garzik.org>
diff --git a/include/linux/libata.h b/include/linux/libata.h
index 65d3187..f7f268e 100644
--- a/include/linux/libata.h
+++ b/include/linux/libata.h
@@ -1151,6 +1151,7 @@
 	qc->nbytes = qc->curbytes = 0;
 	qc->n_elem = 0;
 	qc->err_mask = 0;
+	qc->pad_len = 0;
 
 	ata_tf_init(qc->dev, &qc->tf);