audio/sonic-visualiser: Fix detection using pkg-config with libmad 0.16

Filename for libmad's pc file is now libmad.pc, this broke pkg-config
check however fallback detection code still worked.

Approved by:	portmgr (blanket)

audio/sonic-visualiser/files/patch-configure.ac

@@ -1,6 +1,11 @@
 --- configure.ac.orig	2019-12-10 09:29:11 UTC
 +++ configure.ac
-@@ -127,8 +127,8 @@ SV_MODULE_REQUIRED([mad],[mad >= 0.15.0],[mad.h],[mad]
+@@ -123,12 +123,12 @@ SV_MODULE_OPTIONAL([libpulse],[libpulse >= 0.9],[pulse
+ SV_MODULE_REQUIRED([lrdf],[lrdf >= 0.2],[lrdf.h],[lrdf],[lrdf_init])
+ SV_MODULE_REQUIRED([oggz],[oggz >= 1.0.0],[oggz/oggz.h],[oggz],[oggz_run])
+ SV_MODULE_REQUIRED([fishsound],[fishsound >= 1.0.0],[fishsound/fishsound.h],[fishsound],[fish_sound_new])
+-SV_MODULE_REQUIRED([mad],[mad >= 0.15.0],[mad.h],[mad],[mad_decoder_init])
++SV_MODULE_REQUIRED([mad],[libmad >= 0.15.0],[mad.h],[mad],[mad_decoder_init])
  SV_MODULE_REQUIRED([id3tag],[id3tag >= 0.15.0],[id3tag.h],[id3tag],[id3_tag_new])
  SV_MODULE_REQUIRED([opus],[opusfile],[opus/opusfile.h],[opusfile],[op_read_float])