Fix segfault of qemu-system-arm with PXA target

qemu-system-arm (0.10.5) segfaults when invoked with a PXA machine target,
e.g. -M tosa. The reason is fairly obvious:
Signed-off-by: NTorsten Duwe <duwe@lst.de>
Signed-off-by: NChristoph Hellwig <hch@lst.de>
Signed-off-by: NAndrzej Zaborowski <balrogg@gmail.com>

hw/zaurus.c

@@ -155,7 +155,7 @@ static CPUWriteMemoryFunc *scoop_writefn[] = {
 
 void scoop_gpio_set(void *opaque, int line, int level)
 {
-    ScoopInfo *s = (ScoopInfo *) s;
+    ScoopInfo *s = (ScoopInfo *) opaque;
 
     if (level)
         s->gpio_level |= (1 << line);