graphics/vulkan-loader: restore DISTVERSION after 1461e718a7e0

$ portlint
FATAL: Makefile: PORTVERSION appears out-of-order.
FATAL: Makefile: order must be PORTNAME/PORTVERSION/DISTVERSIONPREFIX/DISTVERSION/DISTVERSIONSUFFIX/PORTREVISION/PORTEPOCH/CATEGORIES/MASTER_SITES/MASTER_SITE_SUBDIR/PROJECTHOST/PKGNAMEPREFIX/PKGNAMESUFFIX/DISTNAME/EXTRACT_SUFX/DISTFILES(_\w+)?/DIST_SUBDIR/EXTRACT_ONLY.
2 fatal errors and 0 warnings found.