fit: If no matching config is found in fit_find_config_node(), use the default one

fit: If no matching config is found in fit_find_config_node(), use the default one

If board_fit_config_name_match() doesn't match any configuration node,
then use the default one (if provided).

Signed-off-by: Jean-Jacques Hiblot <jjhiblot@ti.com>
Reviewed-by: Tom Rini <trini@konsulko.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
(cherry picked from commit 02035d0086b3f9114463a9b9df38a5618ffe8a04)