rtc: rx6110: Convert to SPDX identifier

Use SPDX-License-Identifier instead of a verbose license text.

Signed-off-by: Nobuhiro Iwamatsu <iwamatsu@nigauri.org>
Link: https://lore.kernel.org/r/20191108002250.14937-1-iwamatsu@nigauri.org


Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>