coding guidelines: comply with MISRA C:2012 Rule 9.3

MISRA C:2012 Rule 9.3 (Arrays shall not be partially initialized.)

Systematically use `{0}' to specify full 0 initialization
(not `{}', not `{0U}').

Signed-off-by: Abramo Bagnara <abramo.bagnara@bugseng.com>