pwm: axi-pwmgen: Let .round_waveform_tohw() signal when request was rounded up

The .round_waveform_tohw() is supposed to return 1 if the requested
waveform cannot be implemented by rounding down all parameters. Also
adapt the corresponding comment to better describe why the implemented
procedure is right.

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@baylibre.com>
Tested-by: Trevor Gamblin <tgamblin@baylibre.com>
Link: https://lore.kernel.org/r/ba451573f0218d76645f068cec78bd97802cf010.1743844730.git.u.kleine-koenig@baylibre.com


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