Fix return value in GetDtlsPskCredentials()

Fix return value in GetDtlsPskCredentials()

Fix return value in GetDtlsPskCredentials() from
credresource.c missed in patchset #19785

Change-Id: Id79111409f574ce49f037adb6602a4195666db0c
Signed-off-by: ol.beketov <ol.beketov@samsung.com>
Reviewed-on: https://gerrit.iotivity.org/gerrit/20137
Reviewed-by: Andrii Shtompel <a.shtompel@samsung.com>
Reviewed-by: Dmitriy Zhuravlev <d.zhuravlev@samsung.com>
Reviewed-by: Dan Mihai <Daniel.Mihai@microsoft.com>
Reviewed-by: Kevin Kane <kkane@microsoft.com>
Tested-by: jenkins-iotivity <jenkins@iotivity.org>