Staging: comedi: ni_at_a2150: Remove a few superfluous braces

Please don't flame me :) I'm getting my feet wet with kernel contribution.
One example I saw in a video by GKH suggested cleaning up coding style as a good first commit.

Signed-off-by: Sean Williams <unixed@gmail.com>
Reviewed-by: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>