libubootenv: bump git srcrev

This includes the following changes:

9e121d4 uboot_env: fix print format of type size_t
6c623d1 uboot_env: add ubi volume support
8feae6a uboot_env: add a flag to manage device type
65ae5fe uboot_env: don't accept MTD_DATAFLASH and MTD_UBI_VOLUME
2c36d07 uboot_env: nand: fix return of devwrite
a1744ab uboot_env: nand: fix return of devread

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

recipes-bsp/libubootenv/libubootenv_git.bb

@@ -1,5 +1,5 @@
 require libubootenv.inc
-SRCREV = "88de5d2b0be791f5e91889e8aed5dc985769b74d"
+SRCREV = "9e121d41113dc0313452b2c00627097c46802c10"
 PV_append = "+git${SRCPV}"
 
 DEFAULT_PREFERENCE = "-1"