package/libid3tag: fix id3tag.pc

Add -lz to id3tag.pc, this fix is needed to be able to use pkg-config in
madplay to find id3tag dependencies

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
(cherry picked from commit aa813cd9ac029a8373070ac2c1479dd9aa32ce59)
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

package/libid3tag/id3tag.pc

@@ -8,4 +8,5 @@ Description: ID3 tag reading library
 Version: 0.15.1b
 Requires:
 Libs: -L${libdir} -lid3tag
+Libs.private: -lz
 Cflags: -I${includedir}