Refactor av1_get_mv_class()

Refactored and simplified av1_get_mv_class().

Change-Id: I928f96ffedbd5010f5857d04a83e604ed2950b53
diff --git a/av1/encoder/encodemv.h b/av1/encoder/encodemv.h
index 962844b..4f1c5a6 100644
--- a/av1/encoder/encodemv.h
+++ b/av1/encoder/encodemv.h
@@ -62,9 +62,7 @@
 }
 
 static INLINE MV_CLASS_TYPE av1_get_mv_class(int z, int *offset) {
-  const MV_CLASS_TYPE c = (z >= CLASS0_SIZE * 4096)
-                              ? MV_CLASS_10
-                              : (MV_CLASS_TYPE)av1_log_in_base_2(z >> 3);
+  const MV_CLASS_TYPE c = (MV_CLASS_TYPE)av1_log_in_base_2(z >> 3);
   if (offset) *offset = z - av1_mv_class_base(c);
   return c;
 }