Fix google-explicit-constructor warnings.

Bug: 28341362
Change-Id: I625fbab25f16282c2ea929cd16283d9d146fa17b
diff --git a/media/libmedia/ICrypto.cpp b/media/libmedia/ICrypto.cpp
index 22f8af7..29a0823 100644
--- a/media/libmedia/ICrypto.cpp
+++ b/media/libmedia/ICrypto.cpp
@@ -39,7 +39,7 @@
 };
 
 struct BpCrypto : public BpInterface<ICrypto> {
-    BpCrypto(const sp<IBinder> &impl)
+    explicit BpCrypto(const sp<IBinder> &impl)
         : BpInterface<ICrypto>(impl) {
     }