[HEADERS] One line per header in Kbuild files to reduce conflicts

Signed-off-by: David Woodhouse <dwmw2@infradead.org>
diff --git a/include/rdma/Kbuild b/include/rdma/Kbuild
index eb710ba..e7c0432 100644
--- a/include/rdma/Kbuild
+++ b/include/rdma/Kbuild
@@ -1 +1 @@
-header-y := ib_user_mad.h
+header-y += ib_user_mad.h