libnvdimm, btt: fix btt_rw_page not returning errors

btt_rw_page was not propagating errors frm btt_do_bvec, resulting in any
IO errors via the rw_page path going unnoticed. the pmem driver recently
fixed this in e10624f8 pmem: fail io-requests to known bad blocks
but same problem in BTT went neglected.

Fixes: 5212e11f ("nd_btt: atomic sector updates")
Cc: <stable@vger.kernel.org>
Cc: Toshi Kani <toshi.kani@hpe.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Jeff Moyer <jmoyer@redhat.com>
Signed-off-by: NVishal Verma <vishal.l.verma@intel.com>
Signed-off-by: NDan Williams <dan.j.williams@intel.com>

drivers/nvdimm/btt.c

@@ -1248,10 +1248,13 @@ static int btt_rw_page(struct block_device *bdev, sector_t sector,
 		struct page *page, bool is_write)
 {
 	struct btt *btt = bdev->bd_disk->private_data;
+	int rc;
 
-	btt_do_bvec(btt, NULL, page, PAGE_SIZE, 0, is_write, sector);
-	page_endio(page, is_write, 0);
-	return 0;
+	rc = btt_do_bvec(btt, NULL, page, PAGE_SIZE, 0, is_write, sector);
+	if (rc == 0)
+		page_endio(page, is_write, 0);
+
+	return rc;
 }