Changed the likelihood.

Changed the likelihoood of the mutation and added documentation to the
mutation.

Test: Performed. Ran dexfuzz and waited until mutation kicked in.
Change-Id: I878c1c3434cf17ae8eb1172bf0c326bf15629d5e
diff --git a/tools/dexfuzz/README b/tools/dexfuzz/README
index a635fe9..1f74262 100644
--- a/tools/dexfuzz/README
+++ b/tools/dexfuzz/README
@@ -145,7 +145,7 @@
 PoolIndexChanger 30
 RandomBranchChanger 30
 RandomInstructionGenerator 30
-RegisterClobber 40
+RegisterClobber 10
 SwitchBranchShifter 30
 TryBlockShifter 40
 ValuePrinter 40