Fix harmless warning in dwarf_cfi_to_module.cc

src/common/dwarf_cfi_to_module.cc

Index: src/common/dwarf_cfi_to_module.cc
===================================================================
--- src/common/dwarf_cfi_to_module.cc	(revision 856)
+++ src/common/dwarf_cfi_to_module.cc	(working copy)
@@ -132,7 +132,7 @@
   if (reg == return_address_)
     return ra_name_;
 
-  if (0 <= reg && reg < register_names_.size())
+  if (reg < register_names_.size())
     return register_names_[reg];
 
   reporter_->UnnamedRegister(entry_offset_, reg);