mtl/ofi: fix configury when VPATH is used

Signed-off-by: Gilles Gouaillardet <gilles@rist.or.jp>

ompi/mca/mtl/ofi/Makefile.am

@@ -55,7 +55,7 @@ mtl_ofi_sources = \
 # files should be added to generated_source_modules, as well as adding
 # their .c variants to generated_sources.
 %.c : %.pm;
-	$(PERL) generate-opt-funcs.pl $@
+	$(PERL) -I$(top_srcdir)/ompi/mca/mtl/ofi  $(top_srcdir)/ompi/mca/mtl/ofi/generate-opt-funcs.pl $@
 
 # Make the output library in this directory, and name it either
 # mca_<type>_<name>.la (for DSO builds) or libmca_<type>_<name>.la