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

Avoid undefined behaviour shifting left into the sign bit.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>

hw/intc/xilinx_intc.c

diff --git a/hw/intc/xilinx_intc.c b/hw/intc/xilinx_intc.c
index 4a10398..1b228ff 100644
--- a/hw/intc/xilinx_intc.c
+++ b/hw/intc/xilinx_intc.c
@@ -71,8 +71,9 @@
 
     /* Update the vector register.  */
     for (i = 0; i < 32; i++) {
-        if (p->regs[R_IPR] & (1 << i))
+        if (p->regs[R_IPR] & (1U << i)) {
             break;
+        }
     }
     if (i == 32)
         i = ~0;