[MIPS] Sparse: Use NULL for pointer

This fixes a sparse warning:

arch/mips/kernel/traps.c:376:44: warning: Using plain integer as NULL pointer
Signed-off-by: NAtsushi Nemoto <anemo@mba.ocn.ne.jp>
Signed-off-by: NRalf Baechle <ralf@linux-mips.org>

arch/mips/kernel/traps.c

@@ -373,7 +373,7 @@ asmlinkage void do_be(struct pt_regs *regs)
 		action = MIPS_BE_FIXUP;
 
 	if (board_be_handler)
-		action = board_be_handler(regs, fixup != 0);
+		action = board_be_handler(regs, fixup != NULL);
 
 	switch (action) {
 	case MIPS_BE_DISCARD: