docs: pwm: Adapt Locking paragraph to reality

docs: pwm: Adapt Locking paragraph to reality

We have the distinction between pwm_apply_atomic() and
pwm_apply_might_sleep() since commit c748a6d77c06 (pwm: Rename
pwm_apply_state() to pwm_apply_might_sleep()) contained in v6.8-rc1.

Locking in the core was introduced in commit 1cc2e1faafb3 ("pwm: Add
more locking", contained in v6.13-rc1) to serialize per-chip callbacks
and device removal.

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@baylibre.com>
Link: https://lore.kernel.org/r/20250624100500.1429163-2-u.kleine-koenig@baylibre.com
Signed-off-by: Uwe Kleine-König <ukleinek@kernel.org>