Fix google-explicit-constructor warnings.

Bug: 28341362
Change-Id: I625fbab25f16282c2ea929cd16283d9d146fa17b
diff --git a/media/libmedia/IOMX.cpp b/media/libmedia/IOMX.cpp
index 5423c2a..fbe3f71 100644
--- a/media/libmedia/IOMX.cpp
+++ b/media/libmedia/IOMX.cpp
@@ -61,7 +61,7 @@
 
 class BpOMX : public BpInterface<IOMX> {
 public:
-    BpOMX(const sp<IBinder> &impl)
+    explicit BpOMX(const sp<IBinder> &impl)
         : BpInterface<IOMX>(impl) {
     }
 
@@ -1079,7 +1079,7 @@
 
 class BpOMXObserver : public BpInterface<IOMXObserver> {
 public:
-    BpOMXObserver(const sp<IBinder> &impl)
+    explicit BpOMXObserver(const sp<IBinder> &impl)
         : BpInterface<IOMXObserver>(impl) {
     }