package/edk2-platforms: fix legal-info

Fix typo: EDK2_PLATFORMS_LICENSE_FILE -> EDK2_PLATFORMS_LICENSE_FILES
added by commit 33aa59e7b500e60f2d736a17183c7d49b7baf5bd

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>
(cherry picked from commit 6cd25766163c35b74ba27f08b552bbb92d6bb406)
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

package/edk2-platforms/edk2-platforms.mk

@@ -8,7 +8,7 @@
 EDK2_PLATFORMS_VERSION = db922e1253cb6f1fc456805bc42fb7d401eed5c2
 EDK2_PLATFORMS_SITE = $(call github,tianocore,edk2-platforms,$(EDK2_PLATFORMS_VERSION))
 EDK2_PLATFORMS_LICENSE = BSD-2-Clause
-EDK2_PLATFORMS_LICENSE_FILE = License.txt
+EDK2_PLATFORMS_LICENSE_FILES = License.txt
 EDK2_PLATFORMS_INSTALL_TARGET = NO
 EDK2_PLATFORMS_INSTALL_STAGING = YES