tty: serial: jsm: change the type of local variable

The return type of jsm_get_mstat was int, and the local var result
was for the return should be int, make the change.

This patch fixes the checkpatch.pl warning:
Prefer 'unsigned int' to bare use of 'unsigned'.

Signed-off-by: Gimcuan Hui <gimcuan@gmail.com>
Acked-by: Guilherme G. Piccoli <gpiccoli@linux.vnet.ibm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>