This block of code inconsistently made use of else-if statments. The
patch makes the use consistent. The change also makes the code a bit
simpler to read.
APB12 is never defined as a macro. It is an element in the bus_t enum.
Therefore, the test to check if it is defined will always fail.
APB12 is not a real bus. It is the second register of the APB1 bus. I am
not aware of any STM32 family where the ABP2 bus is implmented (ie
RCC_APB2ENR_SYSCFGEN is defined) and devices attached to said bus are
enabled via the APB1 second register. For this reason, the fix is to
simply remove the check.
The comments still claim STM32F1 support is missing, but this was
recently added.
Also, drop an empty line to fix `too many consecutive empty lines`
nitpick of the CI.
