[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: Atsushi Nemoto <anemo@mba.ocn.ne.jp>
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
1 file changed