pwm: sti: Avoid conditional gotos

[ Upstream commit fd3ae02bb66f091e55f363d32eca7b4039977bf5 ]

Using gotos for conditional code complicates this code significantly.
Convert the code to simple conditional blocks to increase readability.

Suggested-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Acked-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Acked-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Thierry Reding <thierry.reding@gmail.com>
Stable-dep-of: 2d6812b41e0d ("pwm: sti: Reduce number of allocations and drop usage of chip_data")
Signed-off-by: Sasha Levin <sashal@kernel.org>