apps/install Fix PVS381

* Use explicit type cast

Change-Id: I2d75eaeafcb6d46fbc79489394f0f6eb3af6f8d9
Reviewed-on: https://review.haiku-os.org/c/957
Reviewed-by: Adrien Destugues <pulkomandy@gmail.com>

src/apps/installer/CopyEngine.cpp

@@ -576,7 +576,7 @@ CopyEngine::_WriteThread()
 	}
 
 	double megaBytes = (double)fBytesWritten / (1024 * 1024);
-	double seconds = (fTimeWritten / 1000000);
+	double seconds = (double)fTimeWritten / 1000000;
 	if (seconds > 0) {
 		printf("%.2f MB written (%.2f MB/s)\n", megaBytes,
 			megaBytes / seconds);