patch: fix license information

Signed-off-by: Simon Dawson <spdawson@gmail.com>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>

package/patch/patch.mk

@@ -7,6 +7,6 @@
 PATCH_VERSION = 2.7.1
 PATCH_SITE = $(BR2_GNU_MIRROR)/patch
 PATCH_LICENSE = GPLv3+
-PATCH_LICENSE_FILE = COPYING
+PATCH_LICENSE_FILES = COPYING
 
 $(eval $(autotools-package))