[FIRRTL] Whitespace tablegen cleanup, NFC

Cleanup some trailing whitespace in a tablegen file.

Signed-off-by: Schuyler Eldridge <schuyler.eldridge@sifive.com>

include/circt/Dialect/FIRRTL/FIRRTLDeclarations.td

@@ -36,7 +36,7 @@ class ReferableDeclOp<string mnemonic, list<Trait> traits = []> :
 /// located in a hardware-creating context, such as the body of a module.
 class HardwareDeclOp<string mnemonic, list <Trait> traits = []> :
   ReferableDeclOp<mnemonic, traits # [
-    ParentOneOf<[ 
+    ParentOneOf<[
       "firrtl::FModuleOp", "firrtl::LayerBlockOp",
       "firrtl::WhenOp", "firrtl::MatchOp", "sv::IfDefOp"]>]> {}