Input: da9063_onkey - convert header to SPDX

Convert the header of the source file to SPDX.

Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Reviewed-by: Simon Horman <horms+renesas@verge.net.au>
Acked-by: Steve Twiss <stwiss.opensource@diasemi.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>