staging: comedi: s626: remove RR7146 macro

This macro relies on a local variable having a specific name its
also just a wrapper around a readl() call. Remove the macro and
just call readl() directly.

Signed-off-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Reviewed-by: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>