Jetson nano with Jetpack 4.6.1 still uses /boot from SD card

[abishekmuthian]

Describe the issue
Jetson nano with Jetpack 4.6.1 still uses /boot from SDCARD after the copying the rootfs.

When the SDCARD is removed, It's struck in NVIDIA boot splash with SDCARD cross symbol(SDCARD missing).

If SDCARD is present, It uses the USB storage as root from the extlinux.conf from the /boot of SDCARD.

What version of L4T/JetPack
L4T/JetPack version: 4.6.1

Which Jetson
Jetson: Jetson Nano Developer Kit (4GB)

To Reproduce
Steps to reproduce the behavior:
Follow the procedure as per README.md

Expected behavior
It is expected to use the /boot from the USB storage.

Additional context
AFAIK Jetson's bootloader should be able to pickup the USB storage's /boot, but it's not and uses /boot from the SDCARD.