mfd: Correct revision display for WM1811 revision D

As WM1811 revision C was transparent to software the revision IDs for
subsequent revisions are one less than they would normally be. Correct
for this in log messages.

Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Acked-by: Samuel Ortiz <sameo@linux.intel.com>
diff --git a/drivers/mfd/wm8994-core.c b/drivers/mfd/wm8994-core.c
index f9c4016..12bd0ee 100644
--- a/drivers/mfd/wm8994-core.c
+++ b/drivers/mfd/wm8994-core.c
@@ -460,6 +460,11 @@
 			break;
 		}
 		break;
+	case WM1811:
+		/* Revision C did not change the relevant layer */
+		if (ret > 1)
+			ret++;
+		break;
 	default:
 		break;
 	}