Update so we dont use callee saved registers

input/core/itoa.asm

@@ -5,17 +5,14 @@ section .text
     global itoa
 
 itoa:
-    push rbx
-    push rsi
-    push rdx
     mov rax, rdi
     mov rsi, buffer + 19
     mov byte [rsi], 0
     dec rsi
 .loop:
     xor rdx, rdx
-    mov rbx, 10
-    div rbx
+    mov rcx, 10
+    div rcx
     add dl, '0'
     mov [rsi], dl
     dec rsi
@@ -23,7 +20,4 @@ itoa:
     jnz .loop
     inc rsi
     mov rax, rsi
-    pop rdx
-    pop rsi
-    pop rbx
     ret