STM32 I2C: Initialize hz parameter before reset

The hz value is used to compute timeouts,
and timeout are used in reset function, so the parameter needs to be
initialized to its default value before being used.

Author: LMESTM

targets/TARGET_STM/i2c_api.c

@@ -270,12 +270,13 @@ void i2c_init(i2c_t *obj, PinName sda, PinName scl) {
     }
 #endif
 
-    // Reset to clear pending flags if any
-    i2c_reset(obj);
-
     // I2C configuration
+    // Default hz value used for timeout computation
     if(!obj_s->hz)
         obj_s->hz = 100000; // 100 kHz per default
+
+    // Reset to clear pending flags if any
+    i2c_reset(obj);
     i2c_frequency(obj, obj_s->hz );
 
 #if DEVICE_I2CSLAVE