package/shairport-sync: fix static build with libsndfile

package/shairport-sync: fix static build with libsndfile

Fix the following static build failure with libsndfile raise since
commit dbc6e9e9f385995eb10bbfb0bb08e7674100ce66:

/tmp/instance-3/output-1/host/lib/gcc/xtensa-buildroot-linux-uclibc/10.3.0/../../../../xtensa-buildroot-linux-uclibc/bin/ld: /tmp/instance-3/output-1/host/bin/../xtensa-buildroot-linux-uclibc/sysroot/usr/lib/libsndfile.a(libsndfile_la-flac.o): in function `flac_byterate':
flac.c:(.text+0xfc): undefined reference to `FLAC__StreamDecoderErrorStatusString'

Fixes:
 - http://autobuild.buildroot.org/results/92ed30a6855ca11800b779718822bcba4a69c9a3

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>