signal/all/setup_frame remove __put_user checks

Remove "if(__put_user" checks and their related error paths
for all architecture's setup_frame, setup_rt_frame and similar.

Remove the unlock_user_struct when the only way to end up there is
from failed lock_user_struct.

Remove err variable if there are no users for it in the function
anymore.

Signed-off-by: Riku Voipio <riku.voipio@linaro.org>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
