mmc: block: Don't switch to the same partition type in mmc_blk_remove()

It's pointless to switch and trace partition type if the current
selected device partition is the same with that one. Moreover, cycled
claiming host associated with mmc_blk_part_switch() could make
mmc_blk_remove() end up waiting for grabbing the context if it's
occupied, which lead requests could still hit the low-level drivers,
if an asynchronous unbind for host drivers happened, as the card hasn't
been set removed in the remove path.

So a simple dd in background:
dd if=/dev/mmcblk0 of=/dev/null bs=512k count=100000 &

and doing unbind then:
echo fe320000.dwmmc > /sys/bus/platform/drivers/dwmmc_rockchip/unbind

could make the console stuck for quite a while depending on the
numbers of requests.
Suggested-by: Adrian Hunter <adrian.hunter@intel.com>
Signed-off-by: Shawn Lin <shawn.lin@rock-chips.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>

drivers/mmc/core/block.c

@@ -2968,9 +2968,11 @@ static void mmc_blk_remove(struct mmc_card *card)
 	mmc_blk_remove_debugfs(card, md);
 	mmc_blk_remove_parts(card, md);
 	pm_runtime_get_sync(&card->dev);
-	mmc_claim_host(card->host);
-	mmc_blk_part_switch(card, md->part_type);
-	mmc_release_host(card->host);
+	if (md->part_curr != md->part_type) {
+		mmc_claim_host(card->host);
+		mmc_blk_part_switch(card, md->part_type);
+		mmc_release_host(card->host);
+	}
 	if (card->type != MMC_TYPE_SD_COMBO)
 		pm_runtime_disable(&card->dev);
 	pm_runtime_put_noidle(&card->dev);