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/davinci.c b/drivers/usb/musb/davinci.c
index e040d91..bea6cc3 100644
--- a/drivers/usb/musb/davinci.c
+++ b/drivers/usb/musb/davinci.c
@@ -215,7 +215,7 @@
 	 */
 	devctl = musb_readb(mregs, MUSB_DEVCTL);
 	dev_dbg(musb->controller, "poll devctl %02x (%s)\n", devctl,
-		otg_state_string(musb->xceiv->state));
+		usb_otg_state_string(musb->xceiv->state));
 
 	spin_lock_irqsave(&musb->lock, flags);
 	switch (musb->xceiv->state) {
@@ -349,7 +349,7 @@
 		davinci_musb_source_power(musb, drvvbus, 0);
 		dev_dbg(musb->controller, "VBUS %s (%s)%s, devctl %02x\n",
 				drvvbus ? "on" : "off",
-				otg_state_string(musb->xceiv->state),
+				usb_otg_state_string(musb->xceiv->state),
 				err ? " ERROR" : "",
 				devctl);
 		retval = IRQ_HANDLED;