[NFC] fix trivial typos in document and comments

"not not" -> "not" etc

llvm-svn: 330083
diff --git a/llvm/lib/Target/AMDGPU/AMDGPUMachineFunction.h b/llvm/lib/Target/AMDGPU/AMDGPUMachineFunction.h
index 99bb61b..1adf016 100644
--- a/llvm/lib/Target/AMDGPU/AMDGPUMachineFunction.h
+++ b/llvm/lib/Target/AMDGPU/AMDGPUMachineFunction.h
@@ -30,7 +30,7 @@
   /// Start of implicit kernel args
   unsigned ABIArgOffset;
 
-  // Kernels + shaders. i.e. functions called by the driver and not not called
+  // Kernels + shaders. i.e. functions called by the driver and not called
   // by other functions.
   bool IsEntryFunction;