cznic-repo-keys: fix invalid name of key file

The usign has to be in build dependencies to actually use it. It is
possible that package would use `test.pub` as file name for OPKG due to
missing usign.

updater/cznic-repo-keys/Makefile

 #
-## Copyright (C) 2016 CZ.NIC z.s.p.o. (http://www.nic.cz/)
+## Copyright (C) 2016-2022 CZ.NIC z.s.p.o. (http://www.nic.cz/)
 #
 ## This is free software, licensed under the GNU General Public License v2.
 # See /LICENSE for more information.
@@ -8,10 +8,12 @@
 include $(TOPDIR)/rules.mk
 
 PKG_NAME:=cznic-repo-keys
-PKG_VERSION:=4.1
+PKG_VERSION:=4.2
 PKG_RELEASE:=1
 
-PKG_MAINTAINER:=Michal Hrusecky <michal.hrusecky@nic.cz>
+PKG_MAINTAINER:=CZ.NIC <packaging@turris.cz>
+
+PKG_BUILD_DEPENDS:=usign/host
 
 include $(INCLUDE_DIR)/package.mk
 
@@ -31,9 +33,10 @@ define Package/cznic-repo-keys/install
 	$(INSTALL_DIR) $(1)/etc/opkg/keys
 	$(INSTALL_DIR) $(1)/etc/updater/keys/
 	for i in release standby; do \
-		$(CP) files/$$$$i.pub $(1)/etc/opkg/keys/`$(STAGING_DIR_HOST)/bin/usign -F -p files/$$$$i.pub`; \
-		$(CP) files/$$$$i.pub $(1)/etc/updater/keys; \
-		$(CP) files/$$$$i.pub.sig $(1)/etc/updater/keys; \
+		USIGNNAME="$$$$($(STAGING_DIR_HOST)/bin/usign -F -p files/$$$$i.pub)"; \
+		$(CP) files/$$$$i.pub $(1)/etc/opkg/keys/$$$$USIGNNAME; \
+		$(CP) files/$$$$i.pub $(1)/etc/updater/keys/; \
+		$(CP) files/$$$$i.pub.sig $(1)/etc/updater/keys/; \
 	done
 endef
 
@@ -41,16 +44,17 @@ define Package/cznic-repo-keys-test/install
 	$(INSTALL_DIR) $(1)/etc/opkg/keys
 	$(INSTALL_DIR) $(1)/etc/updater/keys/
 	for i in test; do \
-		$(CP) files/$$$$i.pub $(1)/etc/opkg/keys/`$(STAGING_DIR_HOST)/bin/usign -F -p files/$$$$i.pub`; \
-		$(CP) files/$$$$i.pub $(1)/etc/updater/keys; \
-		$(CP) files/$$$$i.pub.sig $(1)/etc/updater/keys; \
+		USIGNNAME="$$$$($(STAGING_DIR_HOST)/bin/usign -F -p files/$$$$i.pub)"; \
+		$(CP) files/$$$$i.pub $(1)/etc/opkg/keys/$$$$USIGNNAME; \
+		$(CP) files/$$$$i.pub $(1)/etc/updater/keys/; \
+		$(CP) files/$$$$i.pub.sig $(1)/etc/updater/keys/; \
 	done
 endef
 
 define Package/cznic-repo-keys/postinst
 #!/bin/sh
 [ -n "$${IPKG_INSTROOT}" ] || {
-# TODO: To remove files, use -r
+# NOTE: To remove files, use -r
 /usr/sbin/cert-backup /etc/updater/keys/release.pub /etc/updater/keys/standby.pub
 }
 endef
@@ -58,7 +62,7 @@ endef
 define Package/cznic-repo-keys-test/postinst
 #!/bin/sh
 [ -n "$${IPKG_INSTROOT}" ] || {
-# TODO: To remove files, use -r
+# NOTE: To remove files, use -r
 /usr/sbin/cert-backup /etc/updater/keys/test.pub
 }
 endef