serial: jsm: some off by one bugs

"brd->nasync" amd "brd->maxports" are the same.  They hold the number of
filled out channels in the brd->channels[] array.  These tests should
be ">=" instead of ">" so that we don't read one element past the end.

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Acked-by: Thadeu Lima de Souza Cascardo <cascardo@linux.vnet.ibm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>