What was the source of your u-boot.bin, and what is your goal? The dd steps to copy and create an image to flash look basically correct, provided the image used to create the dd output is correct, but one part makes me wonder if this is what you actually need.
In particular, you mentioned the dtb blob file, u-boot-dtb-tegra.bin. This is not part of the u-boot.bin executable binary, this remains separate (as an ordinary file, not a partition) and is loaded by the u-boot executable at startup from the /boot directory (this file does not require flash to update). Is this dtb the part you wanted to update?
If it is the dtb you wanted to update or alter, then take a look at /boot/extlinux/extlinux.conf, you’ll see a line “FDT” which is the firmware dtb reference…the path named on this line is how u-boot knows where to find the dtb file. On the assumption that this dtb is what you really want to update, simply put it in /boot with a slightly altered file name from the original and edit this one line in extlinux.conf. If that wasn’t your goal, it would be useful to know what your actual goal is in order to better answer.