Returning ret is wrong. And checking for an error as well. User space
may call multiple times until the work is really scheduled.

twl4030-vibra.c also ignores the return value.
Signed-off-by: H. Nikolaus Schaller <hns@goldelico.com>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>