ubuntu-cpc: Fix ppc64el grub console update

The commit 6dbb30f5 (2.682) which disabled boot splash for all cloud
images introduced an error in the ppc64el hook.  This patch corrects the
name of the variable that contains grub console overrides.  The error
seen during testing was
 'disk-image-ppc64el.binary: line 44: CONSOLES: unbound variable'
and this was due to a typo.

live-build/ubuntu-cpc/hooks.d/base/disk-image-ppc64el.binary

@@ -35,7 +35,7 @@ install_grub() {
     chroot mountpoint apt-get -qqy remove --purge grub-legacy-ec2
 
     # set the kernel commandline to use hvc0
-    CONSOLE="console=hvc0 earlyprintk"
+    CONSOLES="console=hvc0 earlyprintk"
     # Append to the existing GRUB_CMDLINE_LINUX_DEFAULT line
     if [ ! -f mountpoint/etc/default/grub.d/50-cloudimg-settings.cfg ]; then
         echo "Expected to find an existing grub config override"