blink_stm32f4: Fix timer
blink_stm32f4: Fix timer

This example runs using the HSI clock which is 16 MHz. This means
that we need to pass 16 in rather than 25.

I confirmed (with my Logic analyzer) that with this patch that the
timings are correct on the STM32FDISC board which uses an STM32F407.

mcoffin/zinc,richo/zinc,ntwyman/zinc,hackndev/zinc,mcoffin/zinc,ntwyman/zinc,ntwyman/zinc,richo/zinc,mcoffin/zinc,richo/zinc,hackndev/zinc,hackndev/zinc,hackndev/zinc,richo/zinc,ntwyman/zinc,ntwyman/zinc,mcoffin/zinc,mcoffin/zinc,richo/zinc,hackndev/zinc