usb: s/CONFIG_DM_USB/CONFIG_IS_ENABLED(DM_USB)/

This allows to disable the USB driver model in SPL because it checks
the CONFIG_SPL_DM_USB variable for SPL builds. Nothing changes for
regular non-SPL builds.

Signed-off-by: Sven Schwermer <sven@svenschwermer.de>
diff --git a/drivers/usb/musb-new/omap2430.c b/drivers/usb/musb-new/omap2430.c
index 342d76b..58aed72 100644
--- a/drivers/usb/musb-new/omap2430.c
+++ b/drivers/usb/musb-new/omap2430.c
@@ -135,7 +135,7 @@
 	.disable	= omap2430_musb_disable,
 };
 
-#if defined(CONFIG_DM_USB)
+#if CONFIG_IS_ENABLED(DM_USB)
 
 struct omap2430_musb_platdata {
 	void *base;
@@ -276,4 +276,4 @@
 	.priv_auto_alloc_size = sizeof(struct musb_host_data),
 };
 
-#endif /* CONFIG_DM_USB */
+#endif /* CONFIG_IS_ENABLED(DM_USB) */