[llvm-cov] Use the coverage namespace. NFC.

This is a simple code cleanup. It will facilitate moving
LineCoverageIterator to libCoverage.

llvm-svn: 316140
diff --git a/llvm/tools/llvm-cov/SourceCoverageViewText.cpp b/llvm/tools/llvm-cov/SourceCoverageViewText.cpp
index 2ed16df..4b69b08 100644
--- a/llvm/tools/llvm-cov/SourceCoverageViewText.cpp
+++ b/llvm/tools/llvm-cov/SourceCoverageViewText.cpp
@@ -29,8 +29,7 @@
 }
 
 Error CoveragePrinterText::createIndexFile(
-    ArrayRef<std::string> SourceFiles,
-    const coverage::CoverageMapping &Coverage,
+    ArrayRef<std::string> SourceFiles, const CoverageMapping &Coverage,
     const CoverageFiltersMatchAll &Filters) {
   auto OSOrErr = createOutputStream("index", "txt", /*InToplevel=*/true);
   if (Error E = OSOrErr.takeError())