usb: otg: prefix otg_state_string with usb_

all other functions under drivers/usb/ start
with usb_, let's do the same thing.

This patch is in preparation for moving otg_state_string
to usb-common.c and deleting otg.c completely.

Signed-off-by: Felipe Balbi <balbi@ti.com>
diff --git a/drivers/usb/musb/blackfin.c b/drivers/usb/musb/blackfin.c
index dbb31b3..5e63b16 100644
--- a/drivers/usb/musb/blackfin.c
+++ b/drivers/usb/musb/blackfin.c
@@ -280,13 +280,13 @@
 		break;
 	default:
 		dev_dbg(musb->controller, "%s state not handled\n",
-			otg_state_string(musb->xceiv->state));
+			usb_otg_state_string(musb->xceiv->state));
 		break;
 	}
 	spin_unlock_irqrestore(&musb->lock, flags);
 
 	dev_dbg(musb->controller, "state is %s\n",
-		otg_state_string(musb->xceiv->state));
+		usb_otg_state_string(musb->xceiv->state));
 }
 
 static void bfin_musb_enable(struct musb *musb)
@@ -307,7 +307,7 @@
 
 	dev_dbg(musb->controller, "VBUS %s, devctl %02x "
 		/* otg %3x conf %08x prcm %08x */ "\n",
-		otg_state_string(musb->xceiv->state),
+		usb_otg_state_string(musb->xceiv->state),
 		musb_readb(musb->mregs, MUSB_DEVCTL));
 }