libubootenv: bump git SRCREV

This includes the following changes:

88de5d2 uboot_env: access_tostring: fix write once flag
41999c9 README: rework README file
a0ec01c doc: add Buildroot support
5af2a3b uboot_env: fix comment typo
43d6707 uboot_env: remove <pthread.h> header file
6d2abc6 flags are not parsed when environment is loaded
728f047 uboot_env: fix compilation for glibc version >= 2.28
539796c uboot_env: fix build with musl libc
8c07bf0 License: add license file

Signed-off-by: Pierre-Jean Texier <pjtexier@koncepto.io>

recipes-bsp/libubootenv/libubootenv_git.bb

@@ -1,5 +1,5 @@
 require libubootenv.inc
-SRCREV = "edb580a42e46f76543edd0d6fd603881c6294eca"
+SRCREV = "88de5d2b0be791f5e91889e8aed5dc985769b74d"
 PV_append = "+git${SRCPV}"
 
 DEFAULT_PREFERENCE = "-1"