format terminal_writestring() function

kernel.c

@@ -112,9 +112,10 @@ void terminal_putchar(char c) {
  
 void terminal_writestring(const char* data) {
   size_t datalen = strlen(data);
-  for (size_t i = 0; i < datalen; i++)
+  for (size_t i = 0; i < datalen; i++) {
     terminal_putchar(data[i]);
 }
+}
 
 #if defined(__cplusplus)
 extern "C" /* Use C linkage for kernel_main. */