MIPS: Make object accessors more const-correct.

Port r21897 (1b152ae)

Fix MIPS implementation of READ_DOUBLE_FIELD() to use const parameter.

Original commit message:
Getting closer to making our IsFOO and FOO::cast methods
const-correct...

BUG=
R=gergely@homejinni.com, jkummerow@chromium.org

Review URL: https://codereview.chromium.org/344203005

Patch from Balazs Kilvady <kilvadyb@homejinni.com>.

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@21904 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/objects-inl.h

@@ -1175,8 +1175,10 @@ bool JSProxy::HasElementWithHandler(Handle<JSProxy> proxy, uint32_t index) {
       double d;
       uint32_t u[2];
     } c;
-    c.u[0] = (*reinterpret_cast<uint32_t*>(FIELD_ADDR_CONST(p, offset)));
-    c.u[1] = (*reinterpret_cast<uint32_t*>(FIELD_ADDR_CONST(p, offset + 4)));
+    c.u[0] = (*reinterpret_cast<const uint32_t*>(
+        FIELD_ADDR_CONST(p, offset)));
+    c.u[1] = (*reinterpret_cast<const uint32_t*>(
+        FIELD_ADDR_CONST(p, offset + 4)));
     return c.d;
   }
   #define READ_DOUBLE_FIELD(p, offset) read_double_field(p, offset)