drivers: cosmetic: Convert SPDX license tags to Linux Kernel style

Complete in the drivers directory the work started with
commit 83d290c56fab ("SPDX: Convert all of our single
license tags to Linux Kernel style").

Reviewed-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Patrick Delaunay <patrick.delaunay@st.com>
diff --git a/drivers/axi/Makefile b/drivers/axi/Makefile
index 66b6c5a..045db1a 100644
--- a/drivers/axi/Makefile
+++ b/drivers/axi/Makefile
@@ -1,9 +1,8 @@
+# SPDX-License-Identifier: GPL-2.0+
 #
 # (C) Copyright 2017
 # Mario Six,  Guntermann & Drunck GmbH, mario.six@gdsys.cc
 #
-# SPDX-License-Identifier:	GPL-2.0+
-#
 
 obj-$(CONFIG_AXI) += axi-uclass.o
 obj-$(CONFIG_IHS_AXI) += ihs_axi.o