Error 0x0000000000008 On DVMT Patch

[yen eb]

I have intel hd 5500

Downloaded Sierra.app and made installer using Pandora's Box

Patched DSDT and id-platform-id

Installed Sierra successfully without any error

After installing I've seen graphics is 4MB

 

So i got from this forum that i have change DVMT prealloc to 96MB

Extracted BIOS and got the var 0x18C

so with efi shell

tried this

setup_var 0x18C 0x3

and got EFI Error: Can't change efi variable  0x0000000000008

Please help me to fix this

 

PS. Dual Boot Windows 10 and Sierra

Secure Boot off