Save some bytes on printing hexnumbers

lib/print.asm

@@ -1,11 +1,18 @@
 ; important functions in this file: kprintf
 
+; print a word
+; in: ax
+print16:
+  xchg ah,al
+  call print8
+  xchg ah,al
+
 ; print a byte
 ; in: al
 print8:
   push ax ; avoid destroying ah
   push bx
-  mov bx, 0x0000
+  xor bx, bx
   aam 16 ; high nibble moved into ah, low nibble into al
   add ax, 0x3030
   push ax
@@ -24,12 +31,3 @@ print8:
   mov ah, 0x0e
   int 0x10
   ret
-
-; print a word
-; in: ax
-print16:
-  xchg ah,al
-  call print8
-  xchg ah,al
-  call print8
-  ret