dmabufallocator: Fix build if LINUX_DMA_BUF_H is missing

BUG: 148221549
Change-Id: I620f68b0884ef2da341fe4f651a04090ec67e83b

gst-libs/gst/allocators/gstdmabuf.c

diff --git a/gst-libs/gst/allocators/gstdmabuf.c b/gst-libs/gst/allocators/gstdmabuf.c
index e9c5dd3..ec40ea3 100644
--- a/gst-libs/gst/allocators/gstdmabuf.c
+++ b/gst-libs/gst/allocators/gstdmabuf.c
@@ -48,9 +48,10 @@
 gst_dmabuf_mem_map (GstMemory * gmem, GstMapInfo * info, gsize maxsize)
 {
   GstAllocator *allocator = gmem->allocator;
+  gpointer ret;
+
 #ifdef HAVE_LINUX_DMA_BUF_H
   struct dma_buf_sync sync = { DMA_BUF_SYNC_START };
-  gpointer ret;
 
   if (info->flags & GST_MAP_READ)
     sync.flags |= DMA_BUF_SYNC_READ;