staging: comedi: use BIT macro for bit shift operation

This patch silences the Checkpatch.pl warning 'Prefer using the
BIT macro'

Signed-off-by: Hari Prasath Gujulan Elango <hgujulan@visteon.com>
Reviewed-by: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>