usb: Update the test to cover reading and writing

Add test coverage for blk_write() as well.

The blk_erase() is not tested for now as the USB stor interface does not
support erase.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/include/scsi.h b/include/scsi.h
index 94e1d8c..9efefea 100644
--- a/include/scsi.h
+++ b/include/scsi.h
@@ -255,6 +255,16 @@
 	u8 spare2[3];
 };
 
+/** struct scsi_write10_req - data for the write10 command */
+struct __packed scsi_write10_req {
+	u8 cmd;
+	u8 lun_flags;
+	u32 lba;
+	u8 spare;
+	u16 xfer_len;
+	u8 spare2[3];
+};
+
 /**
  * struct scsi_plat - stores information about SCSI controller
  *