comedi: ni_6527: Fix coding style - use BIT macro

BIT macro is used for defining BIT location instead of
shifting operator - coding style issue

Signed-off-by: Ranjith Thangavel <ranjithece24@gmail.com>
Reviewed-by: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>