drivers: i3c: stm32: fix clock init for i2c fast mode plus

The logic of clock initialization for i2c fast mode (FM) and fast
mode plus (FMP) is as follows:
 1 compute how many system clock cycles for SCL to be low
 2 compute how many system clock cycles for SCL to be high by
   subtracting the low duration computed above from the SCL period
 3 verify the high duration computed in 2 is larger than a minimum
The bug is that the step 3 for the FMP is compared with the
minimum value for FM, and causes it to fail.

The fix corrects the bug.

Signed-off-by: Hu Dou <hugh.dou@gmail.com>