[OpenACC][NFC] Fix parse result from 'set'

Apparently 'set' was being parsed as 'shutdown'.  There isn't really any
way of detecting this without getting into a Sema implementation,
however fixing this now as I noticed it.

clang/lib/Parse/ParseOpenACC.cpp

@@ -54,7 +54,7 @@ OpenACCDirectiveKindEx getOpenACCDirectiveKind(Token Tok) {
           .Case("declare", OpenACCDirectiveKind::Declare)
           .Case("init", OpenACCDirectiveKind::Init)
           .Case("shutdown", OpenACCDirectiveKind::Shutdown)
-          .Case("set", OpenACCDirectiveKind::Shutdown)
+          .Case("set", OpenACCDirectiveKind::Set)
           .Case("update", OpenACCDirectiveKind::Update)
           .Case("wait", OpenACCDirectiveKind::Wait)
           .Default(OpenACCDirectiveKind::Invalid);