Fix typo in AMDGPUUsage. NFC (llvm#93652)

The vendor name is mesa but not mesa3d.

Author: SixWeining

llvm/docs/AMDGPUUsage.rst

@@ -64,7 +64,7 @@ to specify the target triple:
      Vendor       Description
      ============ ==============================================================
      ``amd``      Can be used for all AMD GPU usage.
-     ``mesa3d``   Can be used if the OS is ``mesa3d``.
+     ``mesa``     Can be used if the OS is ``mesa3d``.
      ============ ==============================================================
 
   .. table:: AMDGPU Operating Systems