mips: null pointer deref should segfault

Dereferencing a null pointer causes an exception 0xC (EXCP_AdEL)
instead of EXCP_TLBL. This should also trigger a segfault.

Signed-off-by: Wesley W. Terpstra <terpstra@debian.org>
Signed-off-by: Riku Voipio <riku.voipio@linaro.org>

linux-user/main.c

@@ -2120,6 +2120,8 @@ void cpu_loop(CPUMIPSState *env)
             break;
         case EXCP_TLBL:
         case EXCP_TLBS:
+        case EXCP_AdEL:
+        case EXCP_AdES:
             info.si_signo = TARGET_SIGSEGV;
             info.si_errno = 0;
             /* XXX: check env->error_code */