target/hppa: Add MemOp argument to hppa_get_physical_address

Just add the argument, unused at this point.
Zero is the safe do-nothing value for all callers.

Reviewed-by: Helge Deller <deller@gmx.de>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>