Fix a typing error.

I found a typing error on line 82, which typed `long` into `log`. 

fix #780

Initialization/linux-initialization-1.md

@@ -79,7 +79,7 @@ After we sanitized CPU configuration, we call `__startup_64` function which is d
 ```
 
 ```C
-unsigned log __head __startup_64(unsigned long physaddr,
+unsigned long __head __startup_64(unsigned long physaddr,
 				 struct boot_params *bp)
 {
 	unsigned long load_delta, *p;