Update ODROID N2 U-Boot reference to get latest DDR timings (#958)

The DDR timings are taken direclty from the checked out hardkernel
U-Boot tree. Make sure to use the lastest hash to get the latest timing
changes.

buildroot-external/package/hardkernel-boot/hardkernel-boot.mk

@@ -98,7 +98,7 @@ define HARDKERNEL_BOOT_BUILD_CMDS
 endef
 
 else ifeq ($(BR2_PACKAGE_HARDKERNEL_BOOT_ODROID_N2),y)
-HARDKERNEL_BOOT_VERSION = c989da31a5c1da3ab57d7c6dc5a3fdbcc1c3eed7
+HARDKERNEL_BOOT_VERSION = ca5bdd0f1c291d1ec135cd134e01aa2619203d4c
 
 HARDKERNEL_BOOT_BINS += u-boot.g12b
 define HARDKERNEL_BOOT_BUILD_CMDS