ci: Rename defconfig in build.sh

openpower_p9_mambo_defconfig is now called opal_defconfig.

Signed-off-by: Joel Stanley <joel@jms.id.au>
diff --git a/ci/build.sh b/ci/build.sh
index f03b1fb..988fac0 100755
--- a/ci/build.sh
+++ b/ci/build.sh
@@ -45,7 +45,7 @@
       echo ""
       echo "Example:DOCKER_PREFIX=sudo ./ci/build.sh -a"
       echo -e "\tDOCKER_PREFIX=sudo ./ci/build.sh -p firestone"
-      echo -e "\tDOCKER_PREFIX=sudo ./ci/build.sh -p garrison,palmetto,openpower_p9_mambo"
+      echo -e "\tDOCKER_PREFIX=sudo ./ci/build.sh -p garrison,palmetto,opal"
       exit 1
       ;;
     r)