sh4: Fix potential crash in debug code

cppcheck reports this error:

qemu/hw/sh_intc.c:390: error: Possible null pointer dereference:
 s - otherwise it is redundant to check if s is null at line 385

If s were NULL, the printf() statement would crash.
Setting braces fixes this bug.

Signed-off-by: Stefan Weil <weil@mail.berlios.de>
Reviewed-by: Andreas Färber <andreas.faerber@web.de>
Signed-off-by: Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>
