drivers: clock_control: fix AHB2 bus clock activation on stm32f4

During introduction of LL clock_control driver on stm32f4 series,
AHB2 clock activation/deactivation case was let under stm32l4 condition
preventing activation of this clock with F4 series.
This patch fixes the issue.

Change-Id: I5e488e990d33252f491f8960fc7a798ca3416be2
Signed-off-by: Erwan Gouriou <erwan.gouriou@linaro.org>