package/rpi-userland: bump version

Fixes memory leaks due to improper thrads handling.
Fixes to example code.

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

package/rpi-userland/rpi-userland.mk

@@ -4,7 +4,7 @@
 #
 ################################################################################
 
-RPI_USERLAND_VERSION = 5cecd5ae71540a3c11270924251103b3b5c8513a
+RPI_USERLAND_VERSION = 68a2cba184d2726327026429abfe033acf217384
 RPI_USERLAND_SITE = $(call github,raspberrypi,userland,$(RPI_USERLAND_VERSION))
 RPI_USERLAND_LICENSE = BSD-3c
 RPI_USERLAND_LICENSE_FILES = LICENCE