[docs] fix file extension for assembly files

Author: mateoconlechuga

docs/static/asm.rst

@@ -61,7 +61,7 @@ Below is an example C prototype followed by the assembly implementation:
 
     void asm_func(int argument);
 
-:code:`asm_func.asm`
+:code:`asm_func.s`
 
 .. code-block::