w1: omap-hdq: add SPDX tag

Replace GPLv2 license text with SPDX and drop unnecessary file name in
comment to fix checkpatch warnings:

  WARNING: Missing or malformed SPDX-License-Identifier tag in line 1
  WARNING: It's generally not useful to have the filename in the file

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/20230415104304.104134-14-krzysztof.kozlowski@linaro.org


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