clocksource/drivers/digicolor: Convert to SPDX identifier

The license information clearly states GPL version 2 only. The extra text
which excludes warranties is an excerpt of the corresponding GPLv2 clause
11.

So the SPDX identifier covers it completely.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Daniel Lezcano <daniel.lezcano@linaro.org>
Cc: Baruch Siach <baruch@tkos.co.il>
Cc: linux-arm-kernel@lists.infradead.org
Acked-by: Baruch Siach <baruch@tkos.co.il>
Link: https://lore.kernel.org/r/20220510171254.655035023@linutronix.de


Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>