pwm: Fix invalid state detection

pwm: Fix invalid state detection

Commit 9dd42d019e63 ("pwm: Allow pwm state transitions from an invalid
state") intended to allow some state transitions that were not allowed
before. The idea is sane and back then I also got the code comment
right, but the check for enabled is bogus. This resulted in state
transitions for enabled states to be allowed to have invalid duty/period
settings and thus it can happen that low-level drivers get requests for
invalid states🙄.

Invert the check to allow state transitions for disabled states only.

Fixes: 9dd42d019e63 ("pwm: Allow pwm state transitions from an invalid state")
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@baylibre.com>
Link: https://lore.kernel.org/r/20250704172416.626433-2-u.kleine-koenig@baylibre.com
Cc: stable@vger.kernel.org
Signed-off-by: Uwe Kleine-König <ukleinek@kernel.org>