mwifiex: fix SDIO firmware dump problem

It's been observed that firmware doesn't go back to normal
state when all firmware memories are dumped. As a result,
further commands are blocked. This happens due to missing
driver change of writing READ DONE to control register for
SDIO interface.

This patch adds a missing change to fix the problem.

Signed-off-by: Amitkumar Karwar <akarwar@marvell.com>
Signed-off-by: Cathy Luo <cluo@marvell.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>