package/libopenh264: add .hash file

Similar to jquery-keyboard, it seems the libopenh264 tarball on the
autobuilder is corrupt.  Fix it by adding a .hash file so it falls back to
our s.b.o mirror.

Signed-off-by: Romain Naour <romain.naour@gmail.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

package/libopenh264/libopenh264.hash

@@ -0,0 +1,2 @@
+# Locally calculated
+sha256 a1b9a7a7f1ee204793c613789a505f0971bc2b03b3dbd8f05d9c4a3f3b900a22  libopenh264-v1.4.0.tar.gz