Use panic macro where suitable

kern/kalloc.c

@@ -44,7 +44,7 @@ void kfree(void *pa) {
     // Assert that page is a ligned to a page boundary and that its correctly
     // sized
     if (((u64)pa % PGSIZE) != 0 || (char *)pa < kernel_end || (u64)pa >= PHYSTOP)
-        panic("kfree");
+        PANIC("kfree");
 
     // Fill with junk to catch dangling refs.
     memset(pa, 1, PGSIZE);