drivers/gpio: stm32: Check return value of clock_control_on api call

In function gpio_stm32_enable_int, retiurn value of clock_control_on
was not checked.
This is reported as an issue by coverity (CID 219652).
Fix this.

Fixes #33035

Signed-off-by: Erwan Gouriou <erwan.gouriou@linaro.org>