Makefile.am: Do not provide PREFIX value for perl build.

This caused to gain the following error when building:

Only one of PREFIX or INSTALL_BASE can be given. Not both.

Using INSTALLDIRS=vendor is the common way to get the modules installed
into the right directories.

Fixes #12573.
Signed-off-by: Stefan Schantl <stefan.schantl@ipfire.org>
Signed-off-by: Michael Tremer <michael.tremer@ipfire.org>

Makefile.am

@@ -228,7 +228,7 @@ build-perl:
 	@test -e $(builddir)/src/perl/t/Location.t || ln -s --relative $(srcdir)/src/perl/t/Location.t $(builddir)/src/perl/t/
 	@test -e $(builddir)/src/perl/typemap || ln -s --relative $(srcdir)/src/perl/typemap $(builddir)/src/perl/
 
-	cd $(builddir)/src/perl && $(PERL) Makefile.PL PREFIX="$(prefix)" \
+	cd $(builddir)/src/perl && $(PERL) Makefile.PL INSTALLDIRS=vendor \
 		INC="-I$(abs_srcdir)/src" LIBS="-L$(abs_builddir)/src/.libs -lloc"
 	cd $(builddir)/src/perl && $(MAKE) CC="$(CC)" LD="$(LD)" LD_RUN_PATH=