mmc: core: Extend sysfs with DSR register

Export DSR register through sysfs same as we did for the CID, CSD and
OCR registers.

Signed-off-by: Bojan Prtvar <prtvar.b@gmail.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
diff --git a/Documentation/mmc/mmc-dev-attrs.txt b/Documentation/mmc/mmc-dev-attrs.txt
index 8163eca..404a0e9 100644
--- a/Documentation/mmc/mmc-dev-attrs.txt
+++ b/Documentation/mmc/mmc-dev-attrs.txt
@@ -29,6 +29,7 @@
 	raw_rpmb_size_mult	RPMB partition size
 	rel_sectors		Reliable write sector count
 	ocr 			Operation Conditions Register
+	dsr			Driver Stage Register
 
 Note on Erase Size and Preferred Erase Size: