Don't add the file offset twice for trim

We added it when storing the io_piece, don't add it again
when calling trim.

Signed-off-by: Jens Axboe <jaxboe@fusionio.com>
diff --git a/ioengines.c b/ioengines.c
index 7df0aba..e0b0f22 100644
--- a/ioengines.c
+++ b/ioengines.c
@@ -489,7 +489,7 @@
 	struct fio_file *f = io_u->file;
 	int ret;
 
-	ret = os_trim(f->fd, io_u->offset + f->file_offset, io_u->xfer_buflen);
+	ret = os_trim(f->fd, io_u->offset, io_u->xfer_buflen);
 	if (!ret)
 		return io_u->xfer_buflen;;