Since 5f82d17ac6, test-driver scripts
look into top_buildir path, so fix this path on flex's tests/Makefile.
[YOCTO #9721]
(From OE-Core rev: c5da9c7a3c6418386e1f923008e1cd5fbee01fdd)
Signed-off-by: Leonardo Sandoval <leonardo.sandoval.gonzalez@linux.intel.com>
Signed-off-by: Ross Burton <ross.burton@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>