u-boot: update to v2020.10-rc5

Need to step up to a more recent version of U-Boot to make the storing
of U-boot environment variables to work.

Signed-off-by: Joakim Bech <joakim.bech@linaro.org>
diff --git a/default.xml b/default.xml
index db686c6..ee80e04 100644
--- a/default.xml
+++ b/default.xml
@@ -6,7 +6,7 @@
 
 	<project path="linux"   name="torvalds/linux.git"         revision="refs/tags/v5.9"         clone-depth="1" />
         <project path="qemu"    name="qemu/qemu.git"              revision="refs/tags/v5.1.0" />
-        <project path="u-boot"  name="u-boot/u-boot.git"          revision="refs/tags/v2020.07" />
+        <project path="u-boot"  name="u-boot/u-boot.git"          revision="refs/tags/v2020.10-rc5" />
 
         <project path="build"   name="jbech-linaro/build.git" 	  revision="dte" >
                 <linkfile src="Makefile"       dest="Makefile" />