fix bios call, return register values to caller

boot1/src/main.rs

@@ -25,7 +25,7 @@ struct BiosIntr {
 }
 
 unsafe extern "C" {
-  unsafe fn bios_call(intr: u32, args: *mut BiosIntr);
+  unsafe fn _bios_call(intr: u32, args: *mut BiosIntr);
 }
 
 #[panic_handler]
@@ -54,7 +54,7 @@ pub extern "C" fn _start() -> ! {
   };
 
   unsafe {
-    bios_call(0x15, &raw mut args);
+    _bios_call(0x15, &raw mut args);
   }
 
   for (i, b) in STR.iter().copied().enumerate() {