libpayload: Use usb_debug() to show USB messages

Previously printf()'s were used to show USB messages
which results in lots of USB information being shown
when it isn't needed. This will now use the usb_debug()
printing funtion that already exists in usb.h.

Change-Id: I2199814de3327417417eb2e26a660f4a5557cb9f
Signed-off-by: Dave Frodin <dave.frodin@se-eng.com>
Reviewed-on: http://review.coreboot.org/2044
Tested-by: build bot (Jenkins)
Reviewed-by: Anton Kochkov <anton.kochkov@gmail.com>

payloads/libpayload/drivers/usb/uhci.c

@@ -532,7 +532,7 @@ uhci_create_intr_queue (endpoint_t *ep, int reqsize, int reqcount, int reqtiming
 		}
 	}
 	if (nothing_placed) {
-		printf("Error: Failed to place UHCI interrupt queue "
+		usb_debug("Error: Failed to place UHCI interrupt queue "
 			      "head into framelist: no space left\n");
 		uhci_destroy_intr_queue(ep, q);
 		return NULL;