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/fastboot/Makefile b/drivers/fastboot/Makefile
index a242156..048af5a 100644
--- a/drivers/fastboot/Makefile
+++ b/drivers/fastboot/Makefile
@@ -1,4 +1,4 @@
-# SPDX-License-Identifier:      GPL-2.0+
+# SPDX-License-Identifier: GPL-2.0+
 
 obj-y += fb_common.o
 obj-y += fb_getvar.o