Fix some typos in the doc

llvm-svn: 279943
diff --git a/llvm/docs/MemorySSA.rst b/llvm/docs/MemorySSA.rst
index 944df29..0249e70 100644
--- a/llvm/docs/MemorySSA.rst
+++ b/llvm/docs/MemorySSA.rst
@@ -136,7 +136,7 @@
 - ``2 = MemoryDef(6)`` notes that ``store i8 0, i8* %p1`` is a definition,
   and its reaching definition before it is ``6``, or the ``MemoryPhi`` after
   ``while.cond``. (See the `Build-time use optimization`_ and `Precision`_
-  sections below for why this ``MemoryDef`` isn't linked to a seperate,
+  sections below for why this ``MemoryDef`` isn't linked to a separate,
   disambiguated ``MemoryPhi``.)
 - ``3 = MemoryDef(6)`` notes that ``store i8 0, i8* %p2`` is a definition; its
   reaching definition is also ``6``.