Correct SPL uses of CMD_USB

This converts 8 usages of this option to the non-SPL form, since there is
no SPL_CMD_USB defined in Kconfig

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/include/configs/iot2050.h b/include/configs/iot2050.h
index 7d08741..cfff46c 100644
--- a/include/configs/iot2050.h
+++ b/include/configs/iot2050.h
@@ -19,7 +19,7 @@
 #define EXTRA_ENV_IOT2050_BOARD_SETTINGS				\
 	"usb_pgood_delay=900\0"
 
-#if CONFIG_IS_ENABLED(CMD_USB)
+#if IS_ENABLED(CONFIG_CMD_USB)
 # define BOOT_TARGET_USB(func) \
 	func(USB, usb, 0) \
 	func(USB, usb, 1) \