fastboot: Set up fastboot device also for USB_BOOT

Factory software cannot flash if fastboot device is not
set up

Change-Id: I95aa78fa40ac0d56fe6873da7f85ca0855ccb911

drivers/fastboot/fb_fsl/fb_fsl_common.c

diff --git a/drivers/fastboot/fb_fsl/fb_fsl_common.c b/drivers/fastboot/fb_fsl/fb_fsl_common.c
index f7cfec0..a75fe49 100644
--- a/drivers/fastboot/fb_fsl/fb_fsl_common.c
+++ b/drivers/fastboot/fb_fsl/fb_fsl_common.c
@@ -87,6 +87,10 @@
 		break;
 	case USB_BOOT:
 		printf("Detect USB boot. Will enter fastboot mode!\n");
+		dev_no = mmc_get_env_dev();
+		sprintf(boot_dev_part,"mmc%d",dev_no);
+		if (!env_get("fastboot_dev"))
+			env_set("fastboot_dev", boot_dev_part);
 		if (!env_get("bootcmd"))
 			env_set("bootcmd", "fastboot 0");
 		break;