pwm: Mark all devices as "might sleep"

Commit d1cd21427747 ("pwm: Set enable state properly on failed call to
enable") introduced a mutex that is needed to protect internal state of
PWM devices. Since that mutex is acquired in pwm_set_polarity() and in
pwm_enable() and might potentially block, all PWM devices effectively
become "might sleep".

It's rather pointless to keep the .can_sleep field around, but given
that there are external users let's postpone the removal for the next
release cycle.

Signed-off-by: Thierry Reding <[e-mail]>

drivers/pwm/core.c

···
   */
 bool pwm_can_sleep(struct pwm_device *pwm)
 {
-	return pwm->chip->can_sleep;
+	return true;
 }
 EXPORT_SYMBOL_GPL(pwm_can_sleep);