SPDX tag and top of file comment cleanups for the loop driver

Christoph Hellwig
2022-04-19T06:33:09Z

Hi Jens, hi Ted,

the loop driver still had no SPDX tag, so this series cleans up some
lose ends and fixes that up.

Ted, does the SPDX tag match your original licensing decision back then,
or do we need to correct it? Does the auto-converted tag on the loop.h
SPDX header (GPL1.0 or later with syscall exception) make sense, or
should that have been GPL2 only with syscall exception?