staging: line6: replace deprecated strict_strtol() in toneport.c

The LED value is an int, so replace strict_strtol() with kstrtoint().
It's safe to pass in the actual variable instead of a local temporary
because strto*() doesn't write to the result unless the function returns
success.

Signed-off-by: Stefan Hajnoczi <stefanha@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>