mxser: move request irq to probe and switch to managed

Move request_irq from mxser_initbrd to mxser_probe so that we can switch
it to managed request. It simplifies the cleanup code.

Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Link: https://lore.kernel.org/r/20210618061516.662-47-jslaby@suse.cz


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>