PPC: Fix heathrow PIC to use little endian MMIO

During the memory API conversion, the indication on little endianness of
MMIO for the heathrow PIC got dropped. This patch adds it back again.
Signed-off-by: NAlexander Graf <agraf@suse.de>

hw/heathrow_pic.c

@@ -126,7 +126,7 @@ static uint64_t pic_read(void *opaque, target_phys_addr_t addr,
 static const MemoryRegionOps heathrow_pic_ops = {
     .read = pic_read,
     .write = pic_write,
-    .endianness = DEVICE_NATIVE_ENDIAN,
+    .endianness = DEVICE_LITTLE_ENDIAN,
 };
 
 static void heathrow_pic_set_irq(void *opaque, int num, int level)