clocksource/drivers/bcm_kona: Convert to SPDX identifier

The license information clearly states GPL version 2 only. The extra text
which excludes warranties is a transcript of the corresponding GPLv2 clause
11, which is explicitely referenced for details.

So the SPDX identifier covers it completely.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Daniel Lezcano <daniel.lezcano@linaro.org>
Cc: Florian Fainelli <f.fainelli@gmail.com>
Cc: Ray Jui <rjui@broadcom.com>
Cc: Scott Branden <sbranden@broadcom.com>
Cc: Broadcom Kernel Team <bcm-kernel-feedback-list@broadcom.com>
Cc: linux-spdx@vger.kernel.org
Acked-by: Florian Fainelli <f.fainelli@gmail.com>
Link: https://lore.kernel.org/r/20220510171254.404209482@linutronix.de


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