tty: synclink_gt: convert CALC_REGADDR() macro to an inline

tty: synclink_gt: convert CALC_REGADDR() macro to an inline

It makes the code more readable and less error-prone as the result is
returned and not stored in a variable newly defined inside the macro.

Note that cast to 'unsigned long' and back to 'void *' was eliminated as
info->reg_addr is 'char *' already (so the addition is per bytes
already).

This nicely cleans up the callers too.

Signed-off-by: Jiri Slaby (SUSE) <jirislaby@kernel.org>
Link: https://lore.kernel.org/r/20230731090002.15680-2-jirislaby@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>