clk: meson: meson8b: remove spinlock

The spinlock in meson8b clock controller is now only protecting a call to
regmap_update_bits().

The regmap API already has its own locking system so this spinlock
is redundant. Remove it.

Reviewed-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Link: https://lore.kernel.org/r/20240925-clk-meson8b-spinlock-v1-1-50b7f2d02d7d@baylibre.com


[jbrunet: amended to remove unused variable as reported by lkp]
Signed-off-by: Jerome Brunet <jbrunet@baylibre.com>