wimax/i2400m: add CREDITS and MAINTAINERS entries

This patch adds entries for the original developers of the i2400m
drivers and up-to-date maintainer entries.

Signed-off-by: Inaky Perez-Gonzalez <inaky@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>