hw/ide/macio: Fix segfault caused by NULL DMAContext*

Pass qemu_sglist_init the global dma_context_memory rather than a NULL
pointer; this fixes a segfault in dma_memory_map() when the guest
starts using DMA.
Reported-by: NAmadeusz Sławiński <amade@asmblr.net>
Signed-off-by: NPeter Maydell <peter.maydell@linaro.org>
Signed-off-by: NAlexander Graf <agraf@suse.de>

hw/ide/macio.c

@@ -76,7 +76,8 @@ static void pmac_ide_atapi_transfer_cb(void *opaque, int ret)
 
     s->io_buffer_size = io->len;
 
-    qemu_sglist_init(&s->sg, io->len / MACIO_PAGE_SIZE + 1, NULL);
+    qemu_sglist_init(&s->sg, io->len / MACIO_PAGE_SIZE + 1,
+                     &dma_context_memory);
     qemu_sglist_add(&s->sg, io->addr, io->len);
     io->addr += io->len;
     io->len = 0;
@@ -132,7 +133,8 @@ static void pmac_ide_transfer_cb(void *opaque, int ret)
     s->io_buffer_index = 0;
     s->io_buffer_size = io->len;
 
-    qemu_sglist_init(&s->sg, io->len / MACIO_PAGE_SIZE + 1, NULL);
+    qemu_sglist_init(&s->sg, io->len / MACIO_PAGE_SIZE + 1,
+                     &dma_context_memory);
     qemu_sglist_add(&s->sg, io->addr, io->len);
     io->addr += io->len;
     io->len = 0;