__PREFIX__ expands to PREFIX which includes WRKDIR during fake.

One easy fix is to replace it with TRUEPREFIX aka. /usr/local
after the fact;  that fixes startup via desktop menu entries.

I did not see an easy way to pass the proper prefix to just those
.desktop.in files as they seem to be handled during general setup.py
install along with all other files.

Feedback? OK?

Index: Makefile
===================================================================
RCS file: /cvs/ports/net/gpodder/Makefile,v
diff -u -p -r1.39 Makefile
--- Makefile	9 Jan 2024 01:21:47 -0000	1.39
+++ Makefile	8 Feb 2024 10:55:16 -0000
@@ -1,6 +1,7 @@
 COMMENT=		media aggregator and podcast client
 
 MODPY_EGG_VERSION=	3.11.4
+REVISION=		0
 
 GH_ACCOUNT=		gpodder
 GH_PROJECT=		gpodder
@@ -51,6 +52,8 @@ TEST_TARGET=		unittest
 do-install:
 	cd ${WRKSRC} && ${SETENV} ${MAKE_ENV} DESTDIR=/ ${MAKE_PROGRAM} \
 		-f ${MAKE_FILE} install
+	sed -i s,${PREFIX},${TRUEPREFIX}, \
+		${PREFIX}/share/applications/*.desktop
 	${MODPY_BIN} ${MODPY_LIBDIR}/compileall.py \
 		${PREFIX}/share/gpodder/extensions/