[wip/libpointmatcher] fix build in debug

error was:
The configure directory of libpointmatcher-1.3.1~debug could not be found:
	…/robotpkg/wip/libpointmatcher/work.senjosan/libpointmatcher-1.3.1~debug

libpointmatcher/Makefile

@@ -8,7 +8,7 @@ VERSION=		1.3.1
 
 DISTNAME=		${VERSION}
 PKGNAME=		${NAME}-${VERSION}
-WRKSRC=			${WRKDIR}/${PKGNAME}
+WRKSRC=			${WRKDIR}/${NAME}-${VERSION}
 
 HOMEPAGE=		${MASTER_SITE_GITHUB:=${ORG}/${NAME}}
 MASTER_SITES=		${HOMEPAGE}/archive/