MAINTAINERS: update for mwifiex driver maintainers

MAINTAINERS: update for mwifiex driver maintainers

Amit & Nishant would be taking care of maintaining mwifiex driver here
onwards on account of organizational changes.

Signed-off-by: Avinash Patil <patila@marvell.com>
Signed-off-by: Amitkumar Karwar <akarwar@marvell.com>
Signed-off-by: Nishant Sarmukadam <nishants@marvell.com>
Signed-off-by: Cathy Luo <cluo@marvell.com>
Signed-off-by: Frank Huang <frankh@marvell.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>