drop more llvm:: prefixes on SmallString<>

More cleanup after r149799.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@150380 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/tools/driver/driver.cpp b/tools/driver/driver.cpp
index 784b51d..e846b09 100644
--- a/tools/driver/driver.cpp
+++ b/tools/driver/driver.cpp
@@ -388,7 +388,7 @@
   // the installed path. We do this manually, because we want to support that
   // path being a symlink.
   {
-    llvm::SmallString<128> InstalledPath(argv[0]);
+    SmallString<128> InstalledPath(argv[0]);
 
     // Do a PATH lookup, if there are no directory components.
     if (llvm::sys::path::filename(InstalledPath) == InstalledPath) {