drivers: misc: gsc: add support for fan controller

Add support for Gateworks System Controller fan tach input.

Signed-off-by: Tim Harvey <tharvey@gateworks.com>
diff --git a/drivers/misc/gsc.c b/drivers/misc/gsc.c
index dee0bdd..bab405b 100644
--- a/drivers/misc/gsc.c
+++ b/drivers/misc/gsc.c
@@ -330,6 +330,9 @@
 
 			printf("%-8s: %d.%03dV\n", label, val / 1000, val % 1000);
 			break;
+		case 4: /* revolutions per minute */
+			printf("%-8s: %drpm\n", label, val * 30);
+			break;
 		}
 	}