clk: meson: mpll: Delete a useless spinlock from the MPLL

The register corresponding to MPLL does not share the same register
with other module drivers, so there is no concurrent access to the
register with other modules drivers. The spinlock defined in struct
meson_clk_mpll_data is no longer useful.

Signed-off-by: Chuan Liu <chuan.liu@amlogic.com>
Link: https://lore.kernel.org/r/20240925-mpll_spinlock-v2-1-8f9b73588ec1@amlogic.com


Signed-off-by: Jerome Brunet <jbrunet@baylibre.com>