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/fsl_otg.c b/drivers/usb/otg/fsl_otg.c
index 37e8e15..72a2a00 100644
--- a/drivers/usb/otg/fsl_otg.c
+++ b/drivers/usb/otg/fsl_otg.c
@@ -992,7 +992,7 @@
 	/* State */
 	t = scnprintf(next, size,
 		      "OTG state: %s\n\n",
-		      otg_state_string(fsl_otg_dev->phy.state));
+		      usb_otg_state_string(fsl_otg_dev->phy.state));
 	size -= t;
 	next += t;