block/raw-posix: fix FreeBSD compilation

The below patch is needed to compile qemu trunk on FreeBSD with gcc48,
clang will fail.... ;). Host x84_64-freebsd.
Signed-off-by: NAndreas Tobler <andreast@FreeBSD.org>
Signed-off-by: NStefan Hajnoczi <stefanha@redhat.com>

block/raw-posix.c

@@ -1842,7 +1842,8 @@ static BlockDriver bdrv_host_cdrom = {
 #endif /* __linux__ */
 
 #if defined (__FreeBSD__) || defined(__FreeBSD_kernel__)
-static int cdrom_open(BlockDriverState *bs, QDict *options, int flags)
+static int cdrom_open(BlockDriverState *bs, QDict *options, int flags,
+                      Error **errp)
 {
     BDRVRawState *s = bs->opaque;
     Error *local_err = NULL;