mwifiex: don't use [delayed_]work_pending()

Drop work_pending() test from mwifiex_sdio_card_reset().  As
work_pending() becomes %false before sdio_card_reset_worker() starts
executing, it doesn't really protect anything.  reset_host may change
between mmc_remove_host() and mmc_add_host().  Make
sdio_card_reset_worker() cache the target mmc_host so that it isn't
affected by mwifiex_sdio_card_reset() racing with it.

Only compile tested.

Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Bing Zhao <bzhao@marvell.com>
Cc: linux-wireless@vger.kernel.org