osmo-smlc.spec.in:  Add dependency to autoconf-archive

I don't really understand why our other spec files only contain
a dependency to autoconf and get away with that (while still using
autoconf-archive from configure.ac), but let's try this.

Change-Id: Ica5f58297722b650a3862326d31b8eb8947ee1b6
diff --git a/contrib/osmo-smlc.spec.in b/contrib/osmo-smlc.spec.in
index c11bd88..657afc8 100644
--- a/contrib/osmo-smlc.spec.in
+++ b/contrib/osmo-smlc.spec.in
@@ -25,6 +25,7 @@
 URL:            https://osmocom.org/projects/osmo-smlc
 Source:         %{name}-%{version}.tar.xz
 BuildRequires:  autoconf
+BuildRequires:  autoconf-archive
 BuildRequires:  automake >= 1.9
 BuildRequires:  libtool >= 2
 BuildRequires:  pkgconfig >= 0.20