hw/intc/slavio_intctl: Avoid shifting left into sign bit

Add 'U' suffix to avoid undefined behaviour.
Signed-off-by: NPeter Maydell <peter.maydell@linaro.org>
Signed-off-by: NMichael Tokarev <mjt@tls.msk.ru>

hw/intc/slavio_intctl.c

@@ -272,7 +272,7 @@ static void slavio_check_interrupts(SLAVIO_INTCTLState *s, int set_irqs)
             CPU_IRQ_TIMER_IN;
         if (i == s->target_cpu) {
             for (j = 0; j < 32; j++) {
-                if ((s->intregm_pending & (1 << j)) && intbit_to_level[j]) {
+                if ((s->intregm_pending & (1U << j)) && intbit_to_level[j]) {
                     s->slaves[i].intreg_pending |= 1 << intbit_to_level[j];
                 }
             }