package/zerofree: fix legal-info

Fix typo: ZEROFREE_LICENSE_FILE -> ZEROFREE_LICENSE_FILES
added by commit 98ecdd1d1125f2529a8d61c01a2bec6d8dbc48d1

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>

package/zerofree/zerofree.mk

@@ -8,7 +8,7 @@ ZEROFREE_VERSION = 1.1.1
 ZEROFREE_SOURCE = zerofree-$(ZEROFREE_VERSION).tgz
 ZEROFREE_SITE = https://frippery.org/uml
 ZEROFREE_LICENSE = GPL-2.0
-ZEROFREE_LICENSE_FILE = COPYING
+ZEROFREE_LICENSE_FILES = COPYING
 ZEROFREE_DEPENDENCIES = e2fsprogs
 
 # We use the same workaround as in https://bugs.gentoo.org/716136