doc: fix warnings in groups.rst

Add missing '*/', rename <entity> to ENTITY and fix indentation so the
formatting engine recognizes the example code as C code.

Change-Id: Iff1b5c0cef5bb635ba1b39f507ff657e9ab4c338
Signed-off-by: Inaky Perez-Gonzalez <inaky.perez-gonzalez@intel.com>
1 file changed