configure: Use correct variable name in libsnappy test

configure

@@ -4653,7 +4653,7 @@ enabled libopus           && require_pkg_config opus opus_multistream.h opus_mul
 enabled libpulse          && require_pkg_config libpulse-simple pulse/simple.h pa_simple_new
 enabled librtmp           && require_pkg_config librtmp librtmp/rtmp.h RTMP_Socket
 enabled libschroedinger   && require_pkg_config schroedinger-1.0 schroedinger/schro.h schro_init
-enabled libsnappy         && require snappy snappy-c.h snappy_compress -lsnappy
+enabled libsnappy         && require libsnappy snappy-c.h snappy_compress -lsnappy
 enabled libspeex          && require_pkg_config speex speex/speex.h speex_decoder_init -lspeex
 enabled libtheora         && require libtheora theora/theoraenc.h th_info_init -ltheoraenc -ltheoradec -logg
 enabled libtwolame        && require libtwolame twolame.h twolame_init -ltwolame