hw/misc/iotkit-secctl: Fix writing to 'PPC Interrupt Clear' register

hw/misc/iotkit-secctl: Fix writing to 'PPC Interrupt Clear' register

Fix warning reported by Clang static code analyzer:

    CC      hw/misc/iotkit-secctl.o
  hw/misc/iotkit-secctl.c:343:9: warning: Value stored to 'value' is never read
          value &= 0x00f000f3;
          ^        ~~~~~~~~~~

Fixes: b3717c23e1c
Reported-by: Clang Static Analyzer
Signed-off-by: Philippe Mathieu-Daudé <[email protected]>
Message-id: 20200217132922[email protected]
Reviewed-by: Peter Maydell <[email protected]>
Signed-off-by: Peter Maydell <[email protected]>