mmc: core: Update ->card_busy() callback comment

According to SD specification checking state of DAT0 only, is enough while
polling for card busy completion. Let's update the comment in the header
file to correct this, as the comment says DAT[0:3].

Signed-off-by: Mårten Lindahl <marten.lindahl@axis.com>
Link: https://lore.kernel.org/r/20210816153054.24082-1-marten.lindahl@axis.com
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>

include/linux/mmc/host.h

@@ -153,7 +153,7 @@ struct mmc_host_ops {
 
 	int	(*start_signal_voltage_switch)(struct mmc_host *host, struct mmc_ios *ios);
 
-	/* Check if the card is pulling dat[0:3] low */
+	/* Check if the card is pulling dat[0] low */
 	int	(*card_busy)(struct mmc_host *host);
 
 	/* The tuning command opcode value is different for SD and eMMC cards */