pwm: stm32: Use hweight32 in stm32_pwm_detect_channels

[ Upstream commit 41fa8f57

 ]

Use hweight32() to count the CCxE bits in stm32_pwm_detect_channels().
Since the return value is assigned to chip.npwm, change it to unsigned
int as well.

Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Reviewed-by: Fabrice Gasnier <fabrice.gasnier@foss.st.com>
Signed-off-by: Thierry Reding <thierry.reding@gmail.com>
Stable-dep-of: 19f1016e

 ("pwm: stm32: Fix enable count for clk in .probe()")
Signed-off-by: Sasha Levin <sashal@kernel.org>