Fix for calculating CAN timing settings.

NominalPrescaler value needs to be as high as possible to ensure a good approximation of the target CAN speed.
Previous usage of macro IS_FDCAN_DATA_TSEG1 refers to (unsupported by Mbed ) FDCAN CAN controller settings and leads to too low prescaler values.
Usage Macro IS_FDCAN_NOMINAL_TSEG1 yields optimum results.
See also correct macro usage in line #158.

Author: chdelfs

targets/TARGET_STM/can_api.c

@@ -335,7 +335,7 @@ int can_frequency(can_t *obj, int f)
     // !When the sample point should be lower than 50%, this must be changed to
     // !IS_FDCAN_DATA_TSEG2(ntq/nominalPrescaler), since
     // NTSEG2 and SJW max values are lower. For now the sample point is fix @75%
-    while (!IS_FDCAN_DATA_TSEG1(ntq / nominalPrescaler)) {
+    while (!IS_FDCAN_NOMINAL_TSEG1(ntq / nominalPrescaler)) {
         nominalPrescaler ++;
         if (!IS_FDCAN_NOMINAL_PRESCALER(nominalPrescaler)) {
             error("Could not determine good nominalPrescaler. Bad clock value\n");