staging: comedi: dt282x: dt282x_ai_insn_read() always fails

In dt282x_ai_insn_read() we call this macro like:
wait_for(!mux_busy(), comedi_error(dev, "timeout\n"); return -ETIME;);
Because the if statement doesn't have curly braces it means we always
return -ETIME and the function never succeeds.

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Acked-by: Ian Abbott <abbotti@mev.co.uk>
Cc: stable <stable@vger.kernel.org> # 2.6.36+
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>