hw/ide/ahci.c: Avoid shift left into sign bit

Add U suffix to avoid shifting left into the sign bit, which
is undefined behaviour.

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

hw/ide/ahci.c

diff --git a/hw/ide/ahci.c b/hw/ide/ahci.c
index bfe633f..50327ff 100644
--- a/hw/ide/ahci.c
+++ b/hw/ide/ahci.c
@@ -438,9 +438,9 @@
 
     if ((pr->cmd & PORT_CMD_START) && pr->cmd_issue) {
         for (slot = 0; (slot < 32) && pr->cmd_issue; slot++) {
-            if ((pr->cmd_issue & (1 << slot)) &&
+            if ((pr->cmd_issue & (1U << slot)) &&
                 !handle_cmd(s, port, slot)) {
-                pr->cmd_issue &= ~(1 << slot);
+                pr->cmd_issue &= ~(1U << slot);
             }
         }
     }