sdio: initialise SDIO functions and update card->sdio_funcs in lockstep

Daniel Drake noticed a crash in the error path of mmc_attach_sdio().  This
bug is discussed at http://dev.laptop.org/ticket/9707.

BUG: unable to handle kernel paging request at 6b6b6c57
IP: [<b066d6e2>] sdio_remove_func+0x9/0x27
Call Trace:
[<b066cfb4>] ? mmc_sdio_remove+0x34/0x65
[<b066d1fc>] ? mmc_attach_sdio+0x217/0x240
[<b066a22f>] ? mmc_rescan+0x1a2/0x20f
[<b042e9a0>] ? worker_thread+0x156/0x1e

We need to accurately track how many SDIO functions have been initialised
(and keep card->sdio_funcs in sync) so that we don't try to remove more
functions than we initialised if we hit the error path in
mmc_attach_sdio().

Without this patch if we hit the error path in mmc_attach_sdio() we run
the risk of deferencing invalid memory in sdio_remove_func(), leading to a
crash.

Signed-off-by: Matt Fleming <matt@console-pimps.org>
Cc: Daniel Drake <dsd@laptop.org>
Cc: <linux-mmc@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>