The field bcma_nflash::mtd is never set to be non-zero anywhere, but we
test for it in the removal path. So the MTD is never unregistered.

Also, we should use nand_release(), not mtd_device_unregister().

Finally, we don't need to use the 'platdata' for stashing/retrieving our
*driver* data -- that's what *_{get,set}_drvdata() are for.

So, kill off bcm_nflash::mtd, and stash the struct bcm47xxnflash in
drvdata instead. Also move the forward declaration of mtd_info up a bit,
since struct bcma_sflash should be using it.

Caught while inspecting other changes being made to this driver. Compile
tested only.
Signed-off-by: Brian Norris <computersforpeace@gmail.com>
Cc: "Rafał Miłecki" <zajec5@gmail.com>
Cc: linux-wireless@vger.kernel.org
Acked-by: Boris Brezillon <boris.brezillon@free-electrons.com>