mmc: Fix mmc_delay() function

Several fixes for mmc_delay():

 * Repair if-clause that was supposed to detect sub-hz delays.
 * Change yield() to cond_resched() as yield() no longer has the
   semantics we desire.
 * mmc_delay() is used to guarantee protocol delays, so we cannot
   return early (i.e. use _interruptable).

Based on patch by Amol Lad.
Signed-off-by: Pierre Ossman <drzeus@drzeus.cx>

drivers/mmc/mmc.c

@@ -454,11 +454,11 @@ static void mmc_deselect_cards(struct mmc_host *host)
 
 static inline void mmc_delay(unsigned int ms)
 {
-	if (ms < HZ / 1000) {
-		yield();
+	if (ms < 1000 / HZ) {
+		cond_resched();
 		mdelay(ms);
 	} else {
-		msleep_interruptible (ms);
+		msleep(ms);
 	}
 }