pwm: fsl-ftm: Drop driver local locking

The pwm core serializes calls to .apply(), so the driver local lock isn't
needed for that. It only has the effect to serialize .apply() with
.request() and .free() for a different PWM, and .request() and .free
against each other. But given that .request and .free() only do a single
regmap operation under the lock and regmap itself serializes register
accesses, it might happen without the lock that the calls are interleaved
now, but affecting different PWMs, so nothing bad can happen.

So the mutex has no effect and can be dropped.

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@baylibre.com>
Link: https://lore.kernel.org/r/6b72104e5e1823170c7c9664189cc0f2ca5c2347.1750788649.git.u.kleine-koenig@baylibre.com


Signed-off-by: Uwe Kleine-König <ukleinek@kernel.org>