package/libubootenv: bump to version e663439

package/libubootenv: bump to version e663439

Include the following changes:

e663439 Always fsync file writes
80b7f31 Treat '=' as an illegal character in variable names
950f541 libuboot_env: fix calculation of usable envsize
fb88032 Correct initialisations in libuboot_configure
20d1ec7 Force writing of environment if default is used
5ca11bd libuboot_env: correct length to usable env size length
cd4a8f1 libuboot_env_store: fix env double-null termination
9510164 uboot_env: fix infinite loop on short read (EOF)

Signed-off-by: Brandon Maier <brandon.maier@rockwellcollins.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>