mwifiex: fix corner case association failure

This patch corrects the error case in association path by returning
-1. Earlier "media_connected" used to remain on in this error case
causing failure for further association attempts.

Signed-off-by: Amitkumar Karwar <akarwar@marvell.com>
Fixes: b887664d ('mwifiex: channel switch handling for station')
Signed-off-by: Cathy Luo <cluo@marvell.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>