Fix the arguments to memcpy.

Change-Id: Ieaee26f46f43a9d412537047566178985370198b
diff --git a/services/sensorservice/SensorService.cpp b/services/sensorservice/SensorService.cpp
index c8dc6ec..7bc4990 100644
--- a/services/sensorservice/SensorService.cpp
+++ b/services/sensorservice/SensorService.cpp
@@ -1680,7 +1680,7 @@
 #endif
            } else if (numBytesRead == sizeof(uint32_t)) {
                uint32_t numAcks = 0;
-               memcpy(&numAcks, buf, sizeof(numBytesRead));
+               memcpy(&numAcks, buf, numBytesRead);
                // Sanity check to ensure  there are no read errors in recv, numAcks is always
                // within the range and not zero. If any of the above don't hold reset
                // mWakeLockRefCount to zero.