Rename current register allocator implementation

This will allow a cleaner commit in an upcoming
refactoring of register allocation.

Test: m test-art-host

Change-Id: If420c97b088b3c934411ff83373e024003120746
diff --git a/compiler/optimizing/optimizing_compiler.cc b/compiler/optimizing/optimizing_compiler.cc
index d6e09d7..80affc3 100644
--- a/compiler/optimizing/optimizing_compiler.cc
+++ b/compiler/optimizing/optimizing_compiler.cc
@@ -81,7 +81,7 @@
 #include "oat_quick_method_header.h"
 #include "prepare_for_register_allocation.h"
 #include "reference_type_propagation.h"
-#include "register_allocator.h"
+#include "register_allocator_linear_scan.h"
 #include "select_generator.h"
 #include "sharpening.h"
 #include "side_effects_analysis.h"