Fixed typo: 'lenght' in minimal-printf

Note that the word 'lenght' is wrong,
so that 'lenght' should been replaced with 'length'.

Author: DavidLin1577

platform/source/minimal-printf/mbed_printf_implementation.c

@@ -508,7 +508,7 @@ int mbed_minimal_formatted_string(char *buffer, size_t length, const char *forma
                         value = va_arg(arguments, MBED_SIGNED_NATIVE_TYPE);
                     }
 
-                    /* constrict value based on lenght modifier */
+                    /* constrict value based on length modifier */
                     switch (length_modifier) {
                         case LENGTH_NONE:
                             value = (int) value;
@@ -557,7 +557,7 @@ int mbed_minimal_formatted_string(char *buffer, size_t length, const char *forma
                         value = va_arg(arguments, MBED_UNSIGNED_NATIVE_TYPE);
                     }
 
-                    /* constrict value based on lenght modifier */
+                    /* constrict value based on length modifier */
                     switch (length_modifier) {
                         case LENGTH_NONE:
                             value = (unsigned int) value;