clk: meson: fix module license to GPL only

Fix the checkpatch warning:
WARNING: Prefer "GPL" over "GPL v2" - see commit bf7fbeea

 ("module: Cure the MODULE_LICENSE "GPL" vs. "GPL v2" bogosity")

Signed-off-by: Neil Armstrong <neil.armstrong@linaro.org>
Reviewed-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Link: https://lore.kernel.org/r/20240408-amlogic-v6-9-upstream-fix-clk-module-license-v1-1-366ddc0f3db9@linaro.org
Signed-off-by: Jerome Brunet <jbrunet@baylibre.com>