[X86][AMX][NFC] Avoid assert for the same immidiate value

The previous condition in the assert was over strict. We ought to allow
the same immidiate value being loaded more than once. The intention for
the assert is to check the same AMX register uses multiple different
immidiate shapes. So this fix supposes to be NFC.

Reviewed By: LuoYuanke

Differential Revision: https://reviews.llvm.org/D101124