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/otg/isp1301_omap.c b/drivers/usb/otg/isp1301_omap.c
index af9cb11..8fe0c3b 100644
--- a/drivers/usb/otg/isp1301_omap.c
+++ b/drivers/usb/otg/isp1301_omap.c
@@ -236,7 +236,7 @@
 
 static inline const char *state_name(struct isp1301 *isp)
 {
-	return otg_state_string(isp->phy.state);
+	return usb_otg_state_string(isp->phy.state);
 }
 
 /*-------------------------------------------------------------------------*/
@@ -481,7 +481,7 @@
 	if (isp->phy.state == state && !extra)
 		return;
 	pr_debug("otg: %s FSM %s/%02x, %s, %06x\n", tag,
-		otg_state_string(state), fsm, state_name(isp),
+		usb_otg_state_string(state), fsm, state_name(isp),
 		omap_readl(OTG_CTRL));
 }
 
@@ -1077,7 +1077,7 @@
 
 	if (state != isp->phy.state)
 		pr_debug("  isp, %s -> %s\n",
-				otg_state_string(state), state_name(isp));
+				usb_otg_state_string(state), state_name(isp));
 
 #ifdef	CONFIG_USB_OTG
 	/* update the OTG controller state to match the isp1301; may