stagefright amrwb: Change a C++ style cast into a C style cast

This fixes compilation as C - while the source files are named
.cpp, they actually are compileable as pure C (except for this
cast).

This was committed on the master branch of the opencore
repository in commit ae27d9b2ef68c4e6fc383a8cab93d6baa235ff6b,
based on AOSP contribution 10014.

Change-Id: I4f533313be041ad3e0a03ffc5f4207480894ddd1

Author: mstorsjo

media/libstagefright/codecs/amrwb/src/oversamp_12k8_to_16k.cpp

@@ -337,6 +337,6 @@ int16 AmrWbInterpol(                      /* return result of interpolation */
 
     L_sum = shl_int32(L_sum, 2);               /* saturation can occur here */
 
-    return ((int16(L_sum >> 16)));
+    return ((int16)(L_sum >> 16));
 }