CODING_STYLE: specify the indent rule for multiline code

CODING_STYLE: specify the indent rule for multiline code

We didn't specify the indent rule for multiline code here, which may
mislead users. And in current code, the code use various styles.

Add this rule in CODING_STYLE to make sure this is clear to every one.

Signed-off-by: Wei Yang <richardw.yang@linux.intel.com>
Suggested-by: Igor Mammedov <imammedo@redhat.com>
Reviewed-by: Igor Mammedov <imammedo@redhat.com>
Reviewed-by: Stefano Garzarella <sgarzare@redhat.com>
Message-Id: <20190304071631.27567-2-richardw.yang@linux.intel.com>
Signed-off-by: Laurent Vivier <laurent@vivier.eu>