mmc: increase delay when initializing mmc

Running TF-A 2.0 and later seems to cause a regression on HiKey 620.

    NOTICE:  BL2: v2.0(release):v2.0
    NOTICE:  BL2: Built : 17:41:23, Dec 17 2018
    NOTICE:  acpu_dvfs_set_freq: set acpu freq success!ERROR:   CMD1 failed after 100 retries
    ERROR:   BL2: Failed to load image (-5)

The reason seems to be that during emmc enumeration when BL2 sends the command
    OCR_SECTOR_MODE | OCR_VDD_MIN_2V7 | OCR_VDD_MIN_1V7

it for some reason takes some more time to get a reply. So a delay with
mdelay(1), seems to not be enough any longer and therefore we increase it to
mdelay(10) instead which makes the device boot as expected again.
Signed-off-by: Joakim Bech <joakim.bech@linaro.org>

drivers/mmc/mmc.c

@@ -404,7 +404,7 @@ static int mmc_send_op_cond(void)
 			return 0;
 		}
 
-		mdelay(1);
+		mdelay(10);
 	}
 
 	ERROR("CMD1 failed after %d retries\n", SEND_OP_COND_MAX_RETRIES);