mwifiex: change license text from MARVELL to NXP

As of 6-DEC-2019, NXP has acquired Marvell’s Wireless business
unit. This change is to update the license text accordingly.

Signed-off-by: James Cao <zheng.cao@nxp.com>
Signed-off-by: Cathy Luo <xiaohua.luo@nxp.com>
Signed-off-by: Ganapathi Bhat <ganapathi.bhat@nxp.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>