MAINTAINERS: orphan mxser

I cannot maintain this driver for years due to missing HW. Let's orphan
the entry in MAINTAINERS. And likely drop the driver later as these
devices are likely gone from this world. Mxser provides different
(out-of-tree) drivers for their current devices.

Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Link: https://lore.kernel.org/r/20210302062214.29627-1-jslaby@suse.cz


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