fio: fix license

fio does not have any special conditions since version 2.2.6 indeed
MORAL-LICENSE has been updated to replace "promising" by "encouraged"
and "must" by "should":
https://github.com/axboe/fio/commit/67f4822ce3dc6af76b963c6ac467a8f0471a7faf

So fix LICENSE, add MORAL-LICENSE to LICENSE_FILES and add hash for both
licenses

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>

package/fio/fio.hash

@@ -1,2 +1,4 @@
 # Locally computed
 sha256 1952db4d534221e6e8454f851dfcc38328b0ed4a3f499ea25a51ca2b5ccc8136  fio-fio-2.20.tar.gz
+sha256 204d8eff92f95aac4df6c8122bc1505f468f3a901e5a4cc08940e0ede1938994  COPYING
+sha256 8a240c1ad13d1fe3e58588643d81d0695899be4a669fe6d8fafa76ca6a89db2c  MORAL-LICENSE

package/fio/fio.mk

@@ -6,8 +6,8 @@
 
 FIO_VERSION = fio-2.20
 FIO_SITE = git://git.kernel.dk/fio.git
-FIO_LICENSE = GPL-2.0 + special obligations
-FIO_LICENSE_FILES = COPYING
+FIO_LICENSE = GPL-2.0
+FIO_LICENSE_FILES = COPYING MORAL-LICENSE
 
 ifeq ($(BR2_PACKAGE_LIBAIO),y)
 FIO_DEPENDENCIES += libaio