hd-idle: capitalized submenu name (disc -> Disc)

Part of a wider housekeeping effort on the packages repository.

Signed-off-by: Alberto Bursi <alberto.bursi@outlook.it>

utils/hd-idle/Makefile

@@ -27,7 +27,7 @@ define Package/hd-idle
   SECTION:=utils
   CATEGORY:=Utilities
   TITLE:=Another idle-daemon for attached hard drives
-  SUBMENU:=disc
+  SUBMENU:=Disc
   URL:=http://hd-idle.sourceforge.net/
 endef