package/libsndfile: add license hash

Partly fixes:
http://autobuild.buildroot.net/results/f0f/f0fd05ce8a8b595015baf625481b58967df53458/

Signed-off-by: Bernd Kuhls <bernd.kuhls@t-online.de>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

package/libsndfile/libsndfile.hash

@@ -1,2 +1,4 @@
 # Locally calculated after checking pgp signature
 sha256	1ff33929f042fa333aed1e8923aa628c3ee9e1eb85512686c55092d1e5a9dfa9	libsndfile-1.0.28.tar.gz
+# Locally calculated
+sha256	ad01ea5cd2755f6048383c8d54c88459cd6fcb17757c5c8892f8c5ea060f6140	COPYING