Fix inlining switch statement.

Fix inlining switch statement.

In sparse, inline is replacing the function call
expression with a compound statment of inline
function body. During the process, all reference
to the function arguments need to replaced with
calling arguments.

When inlining the case statement. Sparse forgets
to replace the case_label->stmt to the new version.
If it has inner inline function call, it will cause
the orignal copy of the function definition get
modified. That should never happen.

It cause warning error when the inline
function call the second time.

With this change, validations/bug_inline_switch.c
no longer generate warning.

Signed-off-by: Christopher Li <sparse@chrisli.org>