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/otg_fsm.c b/drivers/usb/otg/otg_fsm.c
index ade131a..1f729a1 100644
--- a/drivers/usb/otg/otg_fsm.c
+++ b/drivers/usb/otg/otg_fsm.c
@@ -119,7 +119,7 @@
 	state_changed = 1;
 	if (fsm->otg->phy->state == new_state)
 		return 0;
-	VDBG("Set state: %s\n", otg_state_string(new_state));
+	VDBG("Set state: %s\n", usb_otg_state_string(new_state));
 	otg_leave_state(fsm, fsm->otg->phy->state);
 	switch (new_state) {
 	case OTG_STATE_B_IDLE: