mmc: fix a race between card-detect rescan and clock-gate work instances

Currently there is a race in the MMC core between a card-detect
rescan work and the clock-gating work, scheduled from a command
completion. Fix it by removing the dedicated clock-gating mutex
and using the MMC standard locking mechanism instead.

Signed-off-by: Guennadi Liakhovetski <[e-mail]>
Cc: Simon Horman <[e-mail]>
Cc: Magnus Damm <[e-mail]>
Acked-by: Linus Walleij <[e-mail]>
Cc: <[e-mail]>
Signed-off-by: Chris Ball <[e-mail]>

drivers/mmc/core/host.c

···
 		spin_unlock_irqrestore(&host->clk_lock, flags);
 		return;
 	}
-	mutex_lock(&host->clk_gate_mutex);
+	mmc_claim_host(host);
 	spin_lock_irqsave(&host->clk_lock, flags);
 	if (!host->clk_requests) {
 		spin_unlock_irqrestore(&host->clk_lock, flags);
···
 		pr_debug("%s: gated MCI clock\n", mmc_hostname(host));
 	}
 	spin_unlock_irqrestore(&host->clk_lock, flags);
-	mutex_unlock(&host->clk_gate_mutex);
+	mmc_release_host(host);
 }
 
 /*
···
 {
 	unsigned long flags;
 
-	mutex_lock(&host->clk_gate_mutex);
+	mmc_claim_host(host);
 	spin_lock_irqsave(&host->clk_lock, flags);
 	if (host->clk_gated) {
 		spin_unlock_irqrestore(&host->clk_lock, flags);
···
 	}
 	host->clk_requests++;
 	spin_unlock_irqrestore(&host->clk_lock, flags);
-	mutex_unlock(&host->clk_gate_mutex);
+	mmc_release_host(host);
 }
 
 /**
···
 	host->clk_gated = false;
 	INIT_WORK(&host->clk_gate_work, mmc_host_clk_gate_work);
 	spin_lock_init(&host->clk_lock);
-	mutex_init(&host->clk_gate_mutex);
 }
 
 /**

include/linux/mmc/host.h

···
 	struct work_struct	clk_gate_work; /* delayed clock gate */
 	unsigned int		clk_old;	/* old clock value cache */
 	spinlock_t		clk_lock;	/* lock for clk fields */
-	struct mutex		clk_gate_mutex;	/* mutex for clock gating */
 #endif
 
 	/* host specific block data */