Fix invalid function name in comment

This patch replaces load_corpus_element with the (presumably) correct
function name, load_module_spec, which is defined directly below. This
seems to have been an oversight during a refactoring at some point.

compiler_opt/rl/corpus.py

@@ -386,7 +386,7 @@ def reset(self):
   def sample(self, k: int, sort: bool = False) -> List[ModuleSpec]:
     """Samples `k` module_specs, optionally sorting by size descending.
 
-    Use load_corpus_element to get LoadedModuleSpecs - this allows the user
+    Use load_module_spec to get LoadedModuleSpecs - this allows the user to
     decide how the loading should happen (e.g. may want to use a threadpool)
     """
     # Note: sampler is intentionally defaulted to a mutable object, as the