uninorth: convert ffs(3) to ctz32()

It is not clear from the code how a 0 parameter should be handled by the
hardware.  Keep the same behavior as ffs(0) - 1 == -1.

Cc: Alexander Graf <agraf@suse.de>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Message-id: 1427124571-28598-4-git-send-email-stefanha@redhat.com
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

hw/pci-host/uninorth.c

@@ -92,7 +92,10 @@ static uint32_t unin_get_config_reg(uint32_t reg, uint32_t addr)
         uint32_t slot, func;
 
         /* Grab CFA0 style values */
-        slot = ffs(reg & 0xfffff800) - 1;
+        slot = ctz32(reg & 0xfffff800);
+        if (slot == 32) {
+            slot = -1; /* XXX: should this be 0? */
+        }
         func = (reg >> 8) & 7;
 
         /* ... and then convert them to x86 format */