usb: opiz3: increase USB detect timeout

if the timeout is less than 2.1 seconds, then some flash drives are stratified on the 12 Mb/s bus

Author: alex3696

configs/orangepi_zero3_defconfig

@@ -32,4 +32,4 @@ CONFIG_SPI=y
 CONFIG_USB_EHCI_HCD=y
 CONFIG_USB_OHCI_HCD=y
 CONFIG_USB_MUSB_HOST=y
-CONFIG_PREBOOT="setenv usb_pgood_delay 2000; usb start"
+CONFIG_PREBOOT="setenv usb_pgood_delay 2500; usb start"