qga: 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>
diff --git a/qga/commands-posix.c b/qga/commands-posix.c
index 0dc219d..eae8171 100644
--- a/qga/commands-posix.c
+++ b/qga/commands-posix.c
@@ -16,7 +16,7 @@
 #include <sys/utsname.h>
 #include <sys/wait.h>
 #include <dirent.h>
-#include "qga/guest-agent-core.h"
+#include "guest-agent-core.h"
 #include "qga-qapi-commands.h"
 #include "qapi/error.h"
 #include "qapi/qmp/qerror.h"