staging: clocking-wizard: Contain macro argument in parenthesis

A macro doing some arithmetic to calculate a register offset, did not
contain an argument to the macro in parentheses, potentially leading to
unexpected results when using that macro with arithmetic expressions as
argument.

Signed-off-by: Soren Brinkmann <soren.brinkmann@xilinx.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>