[NFC] Fix typo in CodeGenerator.rst

The file format on z/OS is called GOFF (Generalized Object File Format),
not GCOFF.

Author: redstar

llvm/docs/CodeGenerator.rst

@@ -726,7 +726,7 @@ The table below captures a snapshot of object file support in LLVM:
      ``COFF``            AArch64, ARM, X86
      ``DXContainer``     DirectX
      ``ELF``             AArch64, AMDGPU, ARM, AVR, BPF, CSKY, Hexagon, Lanai, LoongArch, M86k, MSP430, MIPS, PowerPC, RISCV, SPARC, SystemZ, VE, X86
-     ``GCOFF``           SystemZ
+     ``GOFF``            SystemZ
      ``MachO``           AArch64, ARM, X86
      ``SPIR-V``          SPIRV
      ``WASM``            WebAssembly