tty: mxser: improve error handling in mxser_probe() and mxser_module_init()

1. Currently mxser_probe() and mxser_module_init() ignore errors
that can happen in tty_port_register_device().
2. mxser_module_init() does not deallocate resources allocated in mxser_get_ISA_conf()
if mxser_initbrd() failed.

The patch adds proper error handling in all the cases.
Also it moves free_irq() from mxser_release_ISA_res() to mxser_board_remove(),
since it makes mxser_release_ISA_res() a counterpart for mxser_get_ISA_conf(),
while free_irq() is relevant to both ISA and PCI boards.

Found by Linux Driver Verification project (linuxtesting.org).

Signed-off-by: Alexey Khoroshilov <khoroshilov@ispras.ru>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>