Staging: comedi: Prefer using the BIT macro issue in das16.c

This patch Replace all occurences of (1<<x) by BIT(x) in the file das16.c
to get rid of checkpatch.pl "CHECK" output "Prefer using the BIT macro"

Signed-off-by: Ravishankar Karkala Mallikarjunayya <ravishankarkm32@gmail.com>
Reviewed-by: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>