Staging: comedi: ni_at_a2150: remove extra spaces before tab

This patch fix warning given by checkpatch.pl abouts spaces given
before tab

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