devel/premake5: use NO_WRKSUBDIR=yes instead of overriding WRKSRC

When the source archive of a port does not extract into a
subdirectory, the port should set NO_WRKSUBDIR instead of overriding
WRKSRC with WRKDIR.

PR: 288324
Reported by: diizzy (via ports-committers)
Approved by: Martin Filla <freebsd@sysctl.cz> (maintainer)