forked-daapd: Fix build error due to missing gperf

Need to put the build dependency to gperf back, because there is a
bug in forked-daapd 25.0's configure.ac when building without gperf

Signed-off-by: Espen Jürgensen <espenjurgensen+openwrt@gmail.com>

sound/forked-daapd/Makefile

@@ -15,6 +15,7 @@ PKG_SOURCE:=$(PKG_NAME)-$(PKG_VERSION).tar.xz
 PKG_SOURCE_URL:=https://github.com/ejurgensen/$(PKG_NAME)/releases/download/$(PKG_VERSION)/
 PKG_HASH:=5741a64d8f54e11e89dfa2fbfae693b2837e1e19a0c4980a20f8ff56bce4456e
 
+PKG_BUILD_DEPENDS:=gperf/host
 PKG_FIXUP:=autoreconf
 PKG_USE_MIPS16:=0
 PKG_INSTALL:=1