mbed_error: remove redundant memset

If we want zero-fill, strncpy does it anyway.

Author: kjbracey

platform/mbed_error.c

@@ -122,7 +122,6 @@ static mbed_error_status_t handle_error(mbed_error_status_t error_status, unsign
 #if MBED_CONF_PLATFORM_ERROR_FILENAME_CAPTURE_ENABLED
     //Capture filename/linenumber if provided
     //Index for tracking error_filename
-    memset(&current_error_ctx.error_filename, 0, MBED_CONF_PLATFORM_MAX_ERROR_FILENAME_LEN);
     strncpy(current_error_ctx.error_filename, filename, MBED_CONF_PLATFORM_MAX_ERROR_FILENAME_LEN);
     current_error_ctx.error_line_number = line_number;
 #endif