block: use local path for local headers

When pulling in headers that are in the same directory as the C file (as
opposed to one in include/), we should use its relative path, without a
directory.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Tested-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
diff --git a/block/nbd.c b/block/nbd.c
index 3e1693c..ff8333e 100644
--- a/block/nbd.c
+++ b/block/nbd.c
@@ -27,7 +27,7 @@
  */
 
 #include "qemu/osdep.h"
-#include "block/nbd-client.h"
+#include "nbd-client.h"
 #include "qapi/error.h"
 #include "qemu/uri.h"
 #include "block/block_int.h"