wifi: mwifiex: drop redundant device reference

Driver core holds a reference to the USB interface and its parent USB
device while the interface is bound to a driver and there is no need to
take additional references unless the structures are needed after
disconnect.

Drop the redundant device reference to reduce cargo culting, make it
easier to spot drivers where an extra reference is needed, and reduce
the risk of memory leaks when drivers fail to release it.

Signed-off-by: Johan Hovold <johan@kernel.org>
Acked-by: Francesco Dolcini <francesco.dolcini@toradex.com>
Link: https://patch.msgid.link/20260306085144.12064-10-johan@kernel.org
Signed-off-by: Johannes Berg <johannes.berg@intel.com>