i2c: viperboard: return message count on master_xfer success

Returning zero is wrong in this case.

Signed-off-by: Peter Rosin <peda@axentia.se>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>
Fixes: 174a13aa8669 ("i2c: Add viperboard i2c master driver")
diff --git a/drivers/i2c/busses/i2c-viperboard.c b/drivers/i2c/busses/i2c-viperboard.c
index e4be86b..7235c73 100644
--- a/drivers/i2c/busses/i2c-viperboard.c
+++ b/drivers/i2c/busses/i2c-viperboard.c
@@ -337,7 +337,7 @@
 		}
 		mutex_unlock(&vb->lock);
 	}
-	return 0;
+	return num;
 error:
 	mutex_unlock(&vb->lock);
 	return error;