pwm: stm32: Add error messages in .probe()'s error paths

Giving an indication about the problem if probing a device fails is a
nice move. Do that for the stm32 pwm driver.

Reviewed-by: Fabrice Gasnier <fabrice.gasnier@foss.st.com>
Link: https://lore.kernel.org/r/20240315145443.982807-2-u.kleine-koenig@pengutronix.de


Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>