libmad: add license info

[Peter: license is GPLv2+ as pointed out by Arnout]
Signed-off-by: Samuel Martin <s.martin49@gmail.com>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>

package/libmad/libmad.mk

@@ -8,6 +8,8 @@ LIBMAD_VERSION = 0.15.1b
 LIBMAD_SITE = http://downloads.sourceforge.net/project/mad/libmad/$(LIBMAD_VERSION)
 LIBMAD_INSTALL_STAGING = YES
 LIBMAD_LIBTOOL_PATCH = NO
+LIBMAD_LICENSE = GPLv2+
+LIBMAD_LICENSE_FILES = COPYING
 
 define LIBMAD_PREVENT_AUTOMAKE
 	# Prevent automake from running.