Solved.
After recompile the Kernel the display shows the right resolution.
I have to set the fdt_fixup variable anytime when i update the kernel e.g. to change the display timings. To update the Kernal I always use these commands.
run setupdate
run prepare_ubi
run update
setenv fdt_fixup 'fdt addr ${fdt_addr_r} && fdt set /panel compatible "edt,et057090dhu"'
saveenv
boot