MAINTAINERS: update ipwireless entry

Drop the git tree from MAINTAINERS for ipwireless_cs, as there
is no active development on this driver happening. Also change
the driver from Maintained to Odd Fixes for the same reason.

Cc: David Sterba <dsterba@suse.cz>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>