Fixed comment typo.

llvm-svn: 179967
diff --git a/llvm/lib/Transforms/ObjCARC/ObjCARCOpts.cpp b/llvm/lib/Transforms/ObjCARC/ObjCARCOpts.cpp
index ec2fad0..89e7510 100644
--- a/llvm/lib/Transforms/ObjCARC/ObjCARCOpts.cpp
+++ b/llvm/lib/Transforms/ObjCARC/ObjCARCOpts.cpp
@@ -1469,7 +1469,7 @@
       break;
     }
     case IC_RetainBlock:
-      // If we strength reduce an objc_retainBlock to amn objc_retain, continue
+      // If we strength reduce an objc_retainBlock to an objc_retain, continue
       // onto the objc_retain peephole optimizations. Otherwise break.
       if (!OptimizeRetainBlockCall(F, Inst, Class))
         break;