small fix for asm feature warning

Author: luojia65

test-kernel/src/main.rs

@@ -1,5 +1,5 @@
 // A test kernel to test RustSBI function on all platforms
-#![feature(naked_functions, asm, asm_sym, asm_const)]
+#![feature(naked_functions, asm_sym, asm_const)]
 #![feature(default_alloc_error_handler)]
 #![no_std]
 #![no_main]