pwm: stm32-lp: Add check for clk_enable()

Add check for the return value of clk_enable() to catch the potential
error.
We used APP-Miner to find it.

Fixes: e70a540b ("pwm: Add STM32 LPTimer PWM driver")
Signed-off-by: Mingwei Zheng <zmw12306@gmail.com>
Signed-off-by: Jiasheng Jiang <jiashengjiangcool@gmail.com>
Link: https://lore.kernel.org/r/20241206215318.3402860-1-zmw12306@gmail.com


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