azure: Add -E back for the world build script

Commit dd5c954e ("travis/gitlab/azure: Use -W to avoid warnings check")
added -W to avoid warnings check, but it mistakenly dropped -E for
the world build script in the azure pipelines.

This caused builds on the azure pipelines fail to report warnings. Let's
add it back.

Fixes: dd5c954e ("travis/gitlab/azure: Use -W to avoid warnings check")
Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Simon Glass <sjg@chromium.org>