[mlir] Apply ClangTidy fix (NFC)

Prefer to use .empty() instead of checking size() == 0.

Author: akuegel

mlir/lib/AsmParser/AttributeParser.cpp

@@ -309,7 +309,7 @@ ParseResult Parser::parseAttributeDict(NamedAttrList &attributes) {
     else
       return emitWrongTokenError("expected attribute name");
 
-    if (nameId->size() == 0)
+    if (nameId->empty())
       return emitError("expected valid attribute name");
 
     if (!seenKeys.insert(*nameId).second)