drivers/clock_control: stm32: Add AHB3 bus support

AHB3 bus support is added for compatible series.
Additionaly, fix condition for AHB2 support and fix
formatting

Signed-off-by: Erwan Gouriou <erwan.gouriou@linaro.org>
Signed-off-by: Piotr Mienkowski <piotr.mienkowski@gmail.com>