USB: core: move existing SPDX tags to top of the file

To match the rest of the kernel, the SPDX tags for the drivers/usb/core/
files are moved to the first line of the file.  This makes it more
obvious the tag is present as well as making it match the other 12k
files in the tree with this location.

It also uses // to match the "expected style" as well.

Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/core/buffer.c

@@ -1,3 +1,4 @@
+// SPDX-License-Identifier: GPL-2.0
 /*
  * DMA memory management for framework level HCD code (hc_driver)
  *
@@ -5,7 +6,6 @@
  * and should work with all USB controllers, regardless of bus type.
  *
  * Released under the GPLv2 only.
- * SPDX-License-Identifier: GPL-2.0
  */
 
 #include <linux/module.h>