Fix warnings that would be caused by ld flag --warn-common

git-svn-id: svn://svn.savannah.nongnu.org/qemu/trunk@5240 c046a42c-6fe2-441c-8c8c-71466251a162
diff --git a/block.c b/block.c
index d85e27e..15f807a 100644
--- a/block.c
+++ b/block.c
@@ -54,6 +54,8 @@
 static int bdrv_write_em(BlockDriverState *bs, int64_t sector_num,
                          const uint8_t *buf, int nb_sectors);
 
+BlockDriverState *bdrv_first;
+
 static BlockDriver *first_drv;
 
 int path_is_absolute(const char *path)