mwifiex: Allow mwifiex early access to device structure

Today all the interface drivers (usb/pcie/sdio) assign the
adapter->dev in the register_dev() callback, although they
have this piece of info well before hand.

This patch makes the device structure available for mwifiex
right at the beginning, so that it can be used for early
initialization if needed.

This is needed for subsequent patches in this patchset that
intend to unify and consolidate some of the code that would
otherwise have to be duplicated among the interface drivers
(sdio, pcie, usb).

Signed-off-by: Rajat Jain <rajatja@google.com>
Signed-off-by: Amitkumar Karwar <akarwar@marvell.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>