tvheadend: add /etc/tvheadend config to conffiles

Allow backing up and preserving of /etc/tvheadend across sysupgrades.

Signed-off-by: Matthew Hagan <mnhagan88@gmail.com>

multimedia/tvheadend/Makefile

@@ -242,6 +242,7 @@ endef
 
 define Package/tvheadend/conffiles
 /etc/config/tvheadend
+/etc/tvheadend
 endef
 
 define Package/tvheadend/install