flann: add hash file

flann is fetched from Github, so we can add a hash file for this
package.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

package/flann/flann.hash

@@ -0,0 +1,2 @@
+# Locally calculated
+sha256 3fec86866987c792c3fce7ecc8ba9d09a003f5d2d1a1ad94864550aad73a5c0b  flann-3645f0c30a47267e56e5acdecfc7bac2b76bc3d5.tar.gz