staging: unisys: visorinput change -1 return value

This patch changes the vague -1 return value to -EINVAL
Signed-off-by: NErik Arfvidson <erik.arfvidson@unisys.com>
Signed-off-by: NDavid Kershner <david.kershner@unisys.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/unisys/visorinput/visorinput.c

@@ -506,7 +506,7 @@ calc_button(int x)
 	case 3:
 		return BTN_RIGHT;
 	default:
-		return -1;
+		return -EINVAL;
 	}
 }