7seg: fix service file name

The service file name was missing an '@' at the end

Signed-off-by: Benjamin Fair <benjaminfair@google.com>
Change-Id: Ia0dee9d54c2934dcaf3f4891f81a1ca052e217b9
diff --git a/Makefile.am b/Makefile.am
index fd01b4d..c2e7d73 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -9,7 +9,7 @@
 
 if ENABLE_7SEG
 if HAVE_SYSTEMD
-systemdsystemunit_DATA += postcode-7seg.service
+systemdsystemunit_DATA += postcode-7seg@.service
 endif # HAVE_SYSTEMD
 
 bin_PROGRAMS += postcode_7seg