x86emu: Use NULL instead of 0 when assigning pointer

Change-Id: Ie79b9aa79d45dd10c2e5be7f58eed970c243060a
Signed-off-by: Stefan Reinauer <reinauer@google.com>
Reviewed-on: http://review.coreboot.org/1361
Tested-by: build bot (Jenkins)
Reviewed-by: Patrick Georgi <patrick@georgi-clan.de>

src/devices/oprom/x86emu/ops2.c

@@ -336,7 +336,7 @@ static void x86emuOp2_set_byte(u8 op2)
     int mod, rl, rh;
     uint destoffset;
     u8  *destreg;
-    const char *X86EMU_DEBUG_ONLY(name) = 0;
+    const char *X86EMU_DEBUG_ONLY(name) = NULL;
     int cond = 0;
 
     START_OF_INSTR();